Just been reading about this, now from what I can see there isn't the option to do it for desktop but there is for workspaces OK confused yeah I agree, so hopefully this might help.
[opensuse] Workspaces X Wallpapers (KDE4)
I also noticed they said it doesn't save per reboot, as I don't use kde4 I can't test, but I would thought you could have one desktop per workspace<shrug> and if you hibernate just on the occasional reboots you would need to choose them again.
How you would navigate it I dont know(I'm guessing the desktop applet in plasma wouldn't be much good) As for the other again this would be window rules(sticky) and windows place(viewports) again I'm not sure how or even if this is implemented. But...
Compiz Fusion can do both of these and more... KDE4 should of given up with this and just allowed Compiz Fusion to take it all over rather than trying to be a mongrel.
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Man first, have a try at Info, have a look at
Wiki, if all that fails
Scroogle!!!!!
If I've helped click on the Rep button I don't know what it does but it sounds cool.