I will also recommend y to go for Vista Transformation pack 7.
It has almost similar look as Vista. U can downlaod it here:
*vista-transformation-pack.en.softonic.com/
I suggest you first try theming Xp and when you are comfortable with it go for the Transformation pack.I think lot of people have messed up with their pc by using transformation pack.
If deciding on using transformation pack use it in safemode for complete installation.