I spoke way too soon.
Seems that Xandros (default eeePC distro) has 3d enabled, eeeXubuntu does not.
Follow the instructions here for setting up 3d in eeeXubuntu:
http://wiki.eeeuser.com/ubuntu:eeexubuntu:customization
Went from 2FPS to around 18FPS. Dips into single figures in open areas with people.
Open Arena now seems to be 40+ FPS constant - and looks better. Just calling it how I see it.
Maybe with some more hacking I can get this 630Mhz beast to play Nexuiz online and smooth.