Tried that and it turned out Windows wont let me set to different wallpapers for two different monitors if they are in 'extension-mode'. And from what I gathered around the internet, there is no really good (read: easy) way to actually do so. So, I'd have to buy more machines which would probably turn out to be quite expansive.
Honestly, if I could afford it I'd buy most of these wallpapers as posters and get, you know, 'actual wall-papers'.
For now, I think I'll go with cycling backgrounds, even if this means I can admire each singe one just for a short time.
(Oh and no, I didn't actually bought a second monitor to display another wallpaper. Would've been funny though, wouldn't it? xP )