It should (ha!) be easy. The drivers are on the XP CD, and probably also on one of those "automatic" websites that Windows goes to all by itself.
Try removing the printer altogether (via Control Panel etc), then restarting the computer. Sometimes that makes it look again, and it realises it does have the drivers all along.
One of the annoying aspects of Windows is that you can have the right driver, sitting there happily, but it won't take your word for it. It wants to see all the other "stuff" that goes with driver directories. Been there...