The way I look at it, there are too many changes happening almost at once...
First there was DDR2 and within 6 months to a year there will be DDR3 (twice as fast as DDR2 and will cost LESS..!)..., and before you know it "Quad-Core"...
There is no reason, in my mind, to go jumping into a new platform right now until at least DDR3 becomes available and the price of DDR3 compatable systems level off and the usual "Bugs" are worked out of the new MB's/BIOS, etc...
Added to that, there are no G'Cards, AGP OR PCI-E that even come close to saturating the bandwidth available of even AGP... In the future this may happen, but not right NOW...
I could be wrong but, a G'Card like this X1950 Pro/AGP would, at the very Least, let an older system perform at the absolute best it could with out the graphics holding it back. If anything, it would be the CPU that would bottleneck.., but that would mean that you were getting every possible ounce of performance that your system could possibly give you...
That would give someone like me, who really Likes the system he already has, plenty of time to consider a future platform upgrade and LOTS of choices when/if I do and for a reasonable price...
Just my feelings regarding this card and an older AGP system...
\\//_
Edit:
Especially considering that this card can mostlikely be had in the $250 +/- range once it's more available...