Vertex Editing In Radiant, Palette Map
Blitz: The option is "vertex editing splits the polygon" or something. It doesn't actually help the problem, instead it just sends you to vertex editing hell, where all your faces are split into two triangles, and you still can't pull the vertices where you want them, because even with that option enabled it won't let you make an invalid brush.
The way to do the "pipe around a pipe" thing really is as sleepwalkr said, with clipping and face dragging. Maybe I should make a little visual tutorial.
Ricky: Have patience. Also, I found something quake palette related, nice little index of which color is which colormap number.
http://img718.imageshack.us/img718/1070/quakepalette.png