I tried to keep the title post nice and short in the hope that this thread is as long lived as the coding one. So here's a slightly longer one with more information (and also more of my opinions you've heard three times before)

The mdl format was one of the first 3D model formats for games, and naturally is a little less advanced than anything seen today. Here's a rundown of the most important mdl limits:

1000 vertices
2048 triangles
256 frames

The other important limitation of the mdl format is that the vertices are stored with a precision of 8 bits per coordinate axis. The vertices are in effect "snapped" to a grid of 256x256x256 points. This means you can't create intricate detail in your model without it being lost when it moves. It is worth noting that the origin and spacing of this grid can be specified, so the level of detail which can be retained is relative to the overall size of the model.

Editing

One of the greatest barriers to making models for Quake 1 is the lack of good tools. The best tool which works with .mdl format natively at the moment is QMe. You can grab the full 3.0 from:
http://www.fpsbanana.com/tools/2544
and you can upgrade it to version 3.1 with the patch in
http://www.xs4all.nl/~renep/quakeme/qme31_p2.zip

Although QMe is useful for this reason, I'd personally recommend working with the mdl as little as possible. It is generally easier(in my opinion) to create your model in another format entirely, preferably one with a powerful editor which saves the vertices at high precision. Then just export the model to mdl each time you want to test it, much like you compile a new copy of the BSP each time you add to a map.

QuArK ( http://quark.planetquake.gamespy.com/ ) also handles .mdl format natively, as well as other more popular formats such as MD3. I've never been able to use it for any serious editing, but found it a useful tool for converting file formats. So it sits somewhere between working directly with the .mdl and just a waystation for converting files.

If you work in Maya, you are fortunate to have the most direct route to export to .mdl. Lunaren has written:http://lunaran.com/files/lunmodelgen.zip
One package which handles everything directly!

If you work in Blender, you can give a script for exporting to mdl directly a go:
http://www.btinternet.com/~chapterhonour/mdl_export.py
I wrote it a while ago, for blender 2.4.4, and I don't intend to ever revisit it. But it's written in python, so it should be straightforward for people to modify themselves. Alternatively, you can export your model to MD3, using either http://tremx.svn.sourceforge.net/viewvc/tremx/trunk/blender/
or http://cube.wikispaces.com/MD3+Export+From+Blender+Tutorial

Once you have an MD3 of your model, you can run it through QuArK to convert it to mdl. Alternatively (blowing my own trumpet here) you can use "MD3 to MDL"
http://www.btinternet.com/~chapterhonour/md3tomdl.zip
This is my new work in progress, and I welcome any feedback on it. It's a simple command line tool, requiring only a short text file and an MD3 to work from. I'm planning on extending the control file format to include things like model flags, multiple skins, named frame ranges and stuff, so suggestions of what could be useful will not go ignored.

Since MD3 is so well supported amongst editors, you can use the above to get to .mdl format from most major 3d modelling packages. If you don't have any of the more expensive programs (like me), then you could do a lot worse than getting a copy of Gmax. It's a stripped down version of 3d studio max intended for making gaming models, and it's free. Official support for the idea ended a few years ago, and http://www.turbosquid.com/gmax took over distribution. Make sure you also download the Tempest Game Pack, to get the md3 export you will need. Personally, I can't do without gmax...


This thread is pretty much a continuation of http://www.celephais.net/board/view_thread.php?id=60262 , a thread I'd forgotten about until I started researching for this post. Hopefully putting all this information at the top of the thread justifies starting a new one.

Finally, if the low polygon requirements of Q1 seem constraining, take a look at:
http://boards.polycount.net/showthread.php?t=41232
The things some of those posters do with 500 polys are just amazing. 

 

Lunaren's mdl export is at http://lunaran.com/files/lunmodelgen.zip
I previewed to check which links worked, and then messed up actually fixing that one.

Also, to get the ball rolling on actual models, here's a pair of screenshots of the ogre I made ages ago based off metlslime's drawing:
http://www.btinternet.com/~chapterhonour/ogrescr1.jpg
http://www.btinternet.com/~chapterhonour/ogrescr2.jpg
Last time I posted it, it didn't have any blood splatters, and that criticism has been answered. One of the reasons the first version lacked them was that the entire skinmap was mirrored, and so any blood splatter on the chest ended up looking like a rorschach blot. So I carefully unmirrored a few polys here to do the chest.

The other reason I hesitated to do it before is because quite a few of the original id models rely on excessive amounts of blood to mask horrible UV failures. I wanted to make sure this model didn't do that anywhere, which is why the blood is a bit restrained. Hopefully he still looks like a butcher! 

that ogre looks awesome,all it needs is a small amount of blood specks and splashes on its clean face and it will most likely be a widely used replacement 

Thanks for the toppic.
After my own experience with quake models I must say you skinned the Orgue well. In the overall making of models I find the texture part the hardest.

I must admit that if i hadn't had Quark4.07 I couldn't change the dimensions of the model, nor manipulate groups of vertices.

One of my greatest concerns of QMLE is the texture part.
What do I do with tex triangles that are mirrored after imported in Qmle?
If I delete the triangle and patch the vertices again the triangle:

comes back with the same texture, so it's useless work

comes back with a extensive texture subdividing, so texturing can only be done by percisely following the lines untill they make squares. 

Here's how I avoid the problems with the mirrored textures in qme: I don't use qme for that model - at all!

Now this is something I'd like you to try MadFox. Have a go at making a quake model without using qme, and see how it goes. If you don't like it, then that's fair enough. But based on the problems you've posted, I think you will like it. 

feels like asking how to learn riding a bike,
and then say don't use the bike. Start walking.

^^

I don't make the model with Qmle, I'm glad I can import them into Qmle with 3DS files. This goes with an animation programm which is more specificated. I have to change the export to one patch per polygon.
And as it only goes with squads, all triangles get doubled.

Then I'm confronted with importing the New Model from frame.
Saving this first frame also makes my skin frame.

Then I have the choise to turn this first 3DS frame by changing the skin adapture. According the import file it will be a front sight or a side one. So when a triangle gets mirrored I'm delivered to Qmle weary workarounds.

I already tried other ways, but the thing that knocked me out was the import/export to Max3D.
Everytime I seem to get two vertices more by exchanging. 

to put it under a restrictive license.