Themes.

[Vegeta]

You can use some programs to change the appearance of your WindowsXP, though I wouldn't recommend it.

http://www.stardock.com/products/windowblinds/

http://www.lighttek.com/talisman.htm

http://www.tgtsoft.com/prod_sxp.php

Talisman is my favorite, very customizable and very sexy. =0

*doesn't use any of them anymore*

[Metal Koola]

http://www.hamar.sk/sphere/

if you want to turn your desktop into a sphere... pretty cool, but it got annoying fast