In microsoft.com, where do I download desktop themes?

You can browse the themes here: http://www.microsoft.com/windowsxp/downloads/desktop/default.mspx

But I wouldn't use Microsoft themes if I were you. You can find much better themes if you look around. Stardocks has a few programs that lets you customize your desktop and it's free, though it won't have as many functions as the full version on. If you have XP, get WindowBlinds or DesktopX. Then take a look at www.wincustomize.com (http://www.wincustomize.com) to get themes for those. There is also a new version or WindowBlinds (5.5) that works with Vista. Take a look around and you might be suprised at what you see.

I've looked there before, there's a download limit and it won't reset unless I get a premium membership. I didn't know WindowsBlinds was free except for a trial though. Thanks Endless.

I've looked there before, there's a download limit and it won't reset unless I get a premium membership. I didn't know WindowsBlinds was free except for a trial though. Thanks Endless.
I haven't reached my download limit yet, but I remember something saying that if you're a normal member (free) wincustomize will put you into a downloading cue. My WindowBlinds trial hasn't run out let so I can't be certain it's free. But, at www.download.com it says that WindowBlinds is free to use, with limited skinning abilities so my guess is that it will be free.

If you don't like Wincustomize, check out www.deviantart.com. You can also get some skins and themes there.

Under which categories in deviantart?

Category>Customization>Skins and Themes>Windows Utilities>WindowBlinds