Am I the only one to have found the 2.6 kernel making things faster rather than slower compared to 2.4? It has made UI responsiveness superior to 2.4, even when the disk is being heavily utilised. And thats on a single cpu, with hyperthreading or SMP it should really tower over 2.4.
Use hdparm to activate dma, unmaskirq, and 32-bit IO on your harddrive if you havent done so already, all newish systems should support these options and it will make heavy disk operations easier on the system as a whole.
Shutdown anything that will take up ram that you dont need to be active when running planeshift - apache, samba, mysql, bind, whatever, and try using xfce / blackbox or some other light WM rather than full gnome or kde.
MWAAAHAAA, yeah when compiling it yourself you can ditch debug flags and get smaller & faster executables. CrystalSpace in particular benefits a lot from a couple of optimisations due to all the heavy graphics stuff it does.