Well, I know for sure that hosting a UT2004 game is freaking easy. It's easy to follow the way you want it in the Host game. I did try one with 4 people on it...
If you want to host it with a server and let the server spectate, the video card won't need much. It all depends what's the CPU speed and how much CPUs are in it and the Internet speed. At last, the memory comes in. you can go up to 20 people for UT2004. If you're hosting it with 2 servers, gosh...that's too much. you could host three games on 2-3 servers...I wonder why didn't I picked up the server I was told to rip off...perhaps it was because it was a P1 in it...
Three good games elected. If someone doesn't have it, U think the Demo could do it...although...
IMO, I think UT2004, CS:S and WOW OR Battlefield 2 would be great! Hosting a game is via the game itself. Just follow all options and modify the server rules (How many people in it, how long for a time out, how many rounds, etc)