You get the base three with XP Home and Pro... Media Center added a slightly tweaked version of the default Home and Pro theme... But other than that, you have to buy a program like Window Blinds to make use of this feature.
You can get a hacked DLL to let you use some themes, but it's kind of a risky proposition. You never quite know what was done to the file you're putting on your system. Did they only remove the protections, or did they add their own little bit of code to make it easy to slip a trojan or something onto your system? That's aside from it being a violation of the Windows license agreement, and the fact that security updates might replace that file at some point.
Where can I find a cool new theme for my desktop for free? that is not a scam or a trick to go to some BS page!

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