I have this card with AMD-FX 53, 1GB RAM. I am concerned about this card being able to handle newer games. Do you think I'll have a problem? Also, if I upgrade to the X1900, I would have to get a new mobo as well, because I have AGP. Would it be worth the $$ to upgrade at this point?
Personally, I'd recommend the 1900 and a new mobo. You'll have to go to PCIx sometime
The X800XT can handle most games, but looking at games such FEAR/B&W2/COD2 and future releases like Elder Scrolls Oblivion/ STALKER etc a 1900 will see you through the rest of the year - until DX10 starts it reign.
It all boils down to how you enjoy your games and what games you play. Good graphics doesn't always warrant a great game - but in the same breath it adds to overall feeling. If possible, skip the 1800 series, somehow they couldn't tackle games like B&W2 and COD with eye candy enabled - just look at the benches of the 1900's compared to 1800's. The X1800XT might be pardoned here, but the 1900 is more future proof.