If you have mulitple monitors, and setup a dual-screen serverlayout in xorg.conf, you can have multiple desktops with separate icons and wallpapers etc. (edit: I guess it's concievable as well that you could do this with one monitor, but I'm not sure how that would work out in practice /edit)
And you can launch a second x server with a different (or the same) DE/WM as well, if you only have one monitor. It would go something like:
Code:
$startx :1 -layout name.of.layout
but I'm just pulling that out of my ass and it's likely a bit more involved than that (possibly not though, I don't know for sure). if you use the same WM/DE and the same user though, I don't think that will give you ~/Desktop1, ~/Desktop2 etc.