If you had the compatability of xp in win2000 *I would choose 2000, same thing for xp vs vista... vista is *Extremely resource intensive...
If you run comfortable in xp with 1gig, your are going to need at least 2gig with vista, and possible other upgrades if it's been a while since your last...
DELL had an overwhelming flood of complaints when they dropped xp from their line, and had to bring back XP just to prevent loss of sales lol
some pc sites charge 10$ more to put xp home on a machine that would have shipped with vista.
Answers itself ^^
for the common user:
XP 256 ram = capable
XP 512 ram = still slow
(especially with service pack2)
XP 1 gig ram = better
(you will have 750ish ram consumed when doing intensive games/video editing etc.. A Tip - Adjust your virtual memory if your Hard Drive can spare 2 - 3 gig, for a boost -
XP 1.5 gig ram = comfortable
(probably need cpu / mobo upgrade if you are slow with 1.5gig on xp)
XP 2gig ram = more than comfortable =)
*All this varies depending on your cpu & ram types/speeds
(mine is a 1.83ghz 512cache athlon xp - until tax return ^^ [i have ran oc'd at 2.2ghz but this line runs hot so i leave it at 1.83ghz] and have 1.5 gig ram nothing to brag about lol)
*XP shells/start bars can be dropped too for custom low resource shells like geo shell and some others i cant think of right now
& if you want screaming fast read the post above (which leads into a war of which release is best.. kind of.. In my opinion the many different types of linux releases are great! As they are all geared toward specific likings ^^