A lot of my customers have been wondering where they can get free screensavers and desktops for Windows systems. To all of my customers: they typically aren't worth the potential trouble. Spyware and viruses are often hidden in them because they know that the typical Windows user tired long ago of the bouncing "Press Ctrl+Alt+Delete To Log In." As an added disincentive, I've configured Group Policy at most of my sites to prevent changing of the screensaver.
Now that that's out of the way, lets talk about Macdesktops - although it purports to be for Macintosh's, and a lot of desktops are feature Apple logos and themes, the fact is that these are simple images that can be used on any computer desktop!
Once you're at the site, pick a category, find a picture you like, click on the desired resolution (most of my customers are either using 800x600 or 1024x768 - if you not sure, go with 1024x768!), then right-click on the image and choose "set as background." Now you have a new background!