ARGHHH http://www.talkgraphics.com/images/smilies/wink.gif
DPI makes no difference on the web. There is no web standard. An image exported at 72 dpi will download quicker because it's a smaller image than one at 96 dpi. Why not use 10 dpi? This will download even quicker, because it's even smaller.

I don't know what program you used to create your wallpapers, but import one into Xara. Now export it at 72 dpi. It will not be 800 x 600.

Egg