It's a fresh install of Ubuntu 8.10, but the machine only had (256 + 128) MB of memory, so I've just upgraded it and swapped the 128MB DDR out for a 1GB one. Unfortunately my old frame rate of 5fps is now still 5fps

Graphics-card wise it's again a fairly old one (it's an old PC generally), but it's still an NVIDIA with 128MB of memory on it. The game seems to be running without errors, except it's slow and jerky, with as mentioned 5FPS reported rate. Processor is a 1.8GHz Athlon. The only thing I can see that's a bit tight is disc space. There is only 450MB free, although there is a second disk in there and mounted with 7GB left on it.
Any recommendations of things to check or tweak to try and improve matters? The memory reports as working (at least it shows up in the system monitor) and other apps seem to be running a bit better now.