If you are running Win 2K or XP Home/Pro with SP1, the limit is still 2 gigs. With XP Pro & SP2, the limit is 3 gigs -IF- you’ve enabled the 3 gig boot switch, which can be problematic... Photoshopnews.com
I know this will be a big debate but with newer programs comming out there will be no such thing as too much ram. XP doesn't seem to use it now but VISTA will be able to use upto 4gb...supposedly.
I was in the same boat. I had two 512 and bought a 2g set. Now I'm just holding onto it until vista comes out.