WinXp does not have a 3 gig limit it has a 4 gig limit http://support.microsoft.com/kb/294418
with one caveat any ONE application can only use up 2gigs of memory unless its been specifically compile to allow for 3gigs then yeh have to use the /3gb to enable it

http://support.microsoft.com/kb/294418


vista32bit has the same limitation