Honestly, I think the biggest improvement would be to have a 2nd 22" (or just 20") display at 1680x1050 so you can run horizontal span mode. The 22" would look better (same pixel pitch), but either in that resolution would be better. The performance improvement for hoizontal span over dual-view is huge in WinXP. My 8800GTX has disappointing performance in dual-view mode at 1920x1200 & 1680x1050, but I borrowed my roommate's 24" 1920x1200 to test out horizontal span on my machine and it was an unbelievable difference. I ordered a 2nd 24" at 1920x1200 and hope to have it sometime this week.

Memory is so cheap now though.. first maxing out memory to ~3.2GB in 32-bit Windows would be ideal, then plan on your next step from there.