Woh, this is too freaky.
I have the FX5200, and I am looking for a new card for my new system, and I have been thinking abt getting either of those cards.
7900GT - Can be overclocked to a GTX and become the most powerfull card on earth, except that it only has 256MB of RAM wich wont bottleneck it but definetly isnt something u buy for a few years. There is a 512MB edition from Gainward, but trying to find that well, maybe ull have more luck where u live.
X1900XT - Too much Shader power, not enough Texture power. The X1900XT is the exact same card as the XTX except that it costs less (never seen anything like this before.. ATI made a card that it's only difference is it's clockspeed, wich is a very little ammount that u cant even notice). So since the 7900GTX and the X1900XTX are almost the same, u basicly get a 7900GTX from this purchase (with 512MB or ram) without even needing to overclock.
I think the X1900XT is the best, just because its such a huge mistake on ATI's side. Now getting the X1900XT would be an easy choice, IF the prices were the same, but from what i can see, there is a 100$ price difference beetween them. So if u can have the GTX for 100$ less that would be cool, but it has only half the memory and u may not be able to overclock it.
So i think ill get the X1900XT, cause it has so much Shader power, that it makes it "future proof" until DX10.