Performance isn't an issue for me, neither is RAM.
The big issue for me was compatability; both device drivers and software. I had some trouble with some programs running and also some display problems with certain programs. It all works now; except...
There are issues w/ networking the XP machines to the Vista machine; I'm not even sure that it can be done... Vista to Vista = no problems, XP to XP = no problems, Vista to XP = SNAFU. :(

Friends don't let friends use booleans.