tell you what, play ut2003 and a linux box, i've heard that its compatible, and see how it feels.
reason being, linux uses WAY less resources than winxp, that means more hardware power towards playing your game, than background tasks, that you will not be currently using.
i had a friend that did this, he cranked the gfx all the way up on linux, and when he tried it on winxp, he had to tone down the gfx options here and there.