Windows XP comes with a slideshow screensaver which can be pointed at a folder and displays the picture one at a time. For me it refused to display most of my pictures out of about 2000 only 12 would be shown.
On my search to fix this I was unable to find the spec for the photos allowed through the Windows screen saver, I did however discover that google has a screensaver that comes packaged with picasa. This also has and pan & Zoom effect just like the mac screen saver.
Get from :
All you actually need is Picasa, so you can uncheck every thing else if you want.
Once installed you do not have set picasa up just choose the new screensaver from the standard place.