Download this, so you can use custom themes. www.softpedia.com/get/Desktop-Enhancements/Themes/UXTheme-Patch-For-Windows-XP-SP2-Final.shtml The best source for themes is Deviantart Visual Styles, here: http://browse.deviantart.com/customization/skins/windows/visualstyle/
Does this site have any viruses: http://www.themexp.org/. Because I downloaded a theme called Xion into Vista into my laptop (I'm actually using a Desktop now, and it has XP), and it had a virus, it infected the sound in my notebook and I'm scared a virus will come again and I'll get into trouble!
I wouldn't trust theming any Windows OS except by way of custom visual styles/ style packs. Other methods usually are virus-ridden or just very bad for your computer.
My personal view is don't bother, but if you must then avoid stardock programs. They cause a significant performance hit and are not very stable. Straight windows themes are much more reliable than so called 'skinning' programs.