Choosing maps? There are mapvote programs out there of course, Furry has mentioned that one on his server, but I don't know how well it works offline for botmatches. Maybe it does, I dunno.
But this I can tell you.... In UT, the best way to do this,
bar none, was with XMaps. And he's already got a beta out for UT2.
XMaps is designed for use on servers or in botmatches. Using it offline, you can just hit the XMaps button in the middle of your game, and then choose any map, mut, or gametype to play, and 'warp' to it directly. Set the timelimit, fraglimit too. Even choose DM in a CTF map or whatever.
It's BETA, but I've been using it, and it works pretty well. And I am sure it will only get better.
http://www.planetunreal.com/xmaps/
Good stuff.