The most well known site for obtaining Windows XP themes in the past has been ThemeXP.org. The addition of these new servers should help, but if they don't then here is a list of alternative sites where you can find Windows XP themes:
Please note - some sites may contain pop-up advertising.
•Forums at Getskinned.org
(Partial credit for the above list goes to 2kmaro )
If you have any more links to add, or dead links to report, please send the author of this FAQ item an instant message.