Very slow CPU for the amount of RAM it has, though I doubt it's the problem. Don't play on the server you host from unless it's >2.4ghz and has multiple processing cores and the video ram is standalone rather than dependent.
EDIT: I played Tremulous on my other computer (my primary server) which has a 2.4ghz single-core, 512mb RAM and 256mbVideoRam while the high-speed 120gb HDD did most of the work. Played fine, dunno what your problem is.
Sorry I can't help more.