it depends, a dedicated LAN servers requirements varies from game to game, but I would say for CS, COD, & Warcraft 3, it should work fine, those are all older games, not sure about Halo, but it should, as to UT2004, not sure on that.
the thing that might hurt you on some of the games, is the 512MB of system RAM, its not bottom of the barrel, but could use a bit more, if it were me, I'd have no less than 768MB, but then again, it all depends on the games being run. (and whatever else is installed & running on the server as well, besides the OS)
probably the best thing to do, is figure out which games you want to run, then narrow those down by looking up their mimimum specs required, either for the game itself, or if there are minimum server specs listed somewhere.