ive got Slackware 10 and it certainly runs America's Army far faster than my old Suse distro did. ur better off making sure Fluxbox or a similar basic X-based GUI is installed so u can use KDE/Gnome for ur normal desktop use and Flubox/Blackbox or similar for games, ull be amazed at what a difference a simple GUI can make.
Native linux games tend to be very good (America's Army, Enemy Territory, Doom 3 and so forth) but for a wider range u will have to use Cedega (WineX's new monicker) to play Windows games, they will almost certainly still play at a high fps.
for games in general tho i would recommend a more advanced distro such as Slackware or Debian, just so it can be optimised for speed and low memory/CPU usage. just look at how slow Windows XP games can run!