I would say postphoning will be a wise decision. It'll save u money and moreover with the Microsoft Vista being launched, upgrading ur PC accordingly will be a good decision.
Vista will have DirectX 10 support which is not in XP and newer games will require DirextX 10 compliant Graphic cards.
See the link !
Hope it helps !
I think my earlier query has been solved. And the new subject would deviate from the main one. So, I request the moderator of the forum to close this thread and avoid unnecessary lengthening of a good thread.