Been looking for the same sort of thing.
Just heard of it and I'm downloading it immediatley. I've seen a lot of referances to a program called 'Valve Hammer' used for creating BSP maps. Judging from what I've read in these forums BSP seems to cause more problems than it solves. It seems to require a lot of 'work arounds' just to get it working.
I eventually decided to write my own (after 3 false starts), that way I can be sure it exports all of the data I need in a format I understand. It's a big job and I'm only about 30% through it, but I've learned a lot along the way, and most of the code will be reusable in my game, so I'd say it's worth doing for yourself.
Lot's of articles about game programming techniques explain that most games start life as a level editor and grow outward from that. When a programming team start their next project they spend a lot of time expanding and modifying their old level editor to suit thier new game.
Go on dive in!