Straight from Chris Pirillo's site:
[...] since Windows Vista supports JPG wallpapers, you should no longer set your wallpaper through Internet Explorer (which converts images to BMP before they’re set to your desktop, totally nullifying any kind of improvement the Vista shell team did in respect to saving system resources). Here’s how I’d suggest doing it from this point forward.
- When you find a suitable wallpaper image on the Web through Internet Explorer, don’t right-click and “Set as background” like you’ve done in the past.
- Instead, right-click your desktop and “Personalize” - then select “Desktop Background” from the list of options in that panel.
- Drag and drop the image you like in IE into the scrolling frame of the Desktop Background panel. It’ll automatically copy the image from your browser to your computer.
- Consider browsing to a different folder on your machine before dragging and dropping images from IE to the Desktop Background applet.
- From there, you can set the image as your wallpaper at will. It should remain in the JPG format, which is what you want.
