While im glad that you're showing an interest in mapping, I'm pretty stunned that you couldn't find anything about how to make maps on DP. I mean, did you even look in the Mapping section?
anyway, download the custom version of BSP off here:
http://digitalpaint.planetquake.gamespy.com/files/ (you can also use quark, but I wouldn't know too much about that).
and use all the links lekky just beat me to posting. Also, please please please read the gamedesign.net stuff on VIS'ing and pay attention to r_speeds for the sake of my sanity.
Good luck,
- Dr Rick Dagless M.D