I tried to upgrade the mother board in my XPS400, to a later DELL model,
but it would not fit (I couldn't find any 3d party mfg. that would fit in a DELL?).
My Upgrades that REALLY worked!-
1. I upgraded to 4 gig (2gig x 2 is best!) of "matching" Crucial memory (Dual channel!). Helped some.
2. I then upgraded my C: hard drive to a Western Digital Raptor 10k rpm Hard Drive!
WOW!- My computer is now BLAZING FAST!