Sality is what is technically known as a polymorphic file infector - or Fred to it's friends. The polymorphic part means that the code morphs during the infection process in an attempt to adopt a form that scanners haven't identified as malicious and hence will be left alone by said scanners. The infector part is pretty much what it says, it targets Windows executable files with extensions .SCR or .EXE.
The problem that you have in dealing with it is in identifying every infected file and removing it before they can infect further files while at the same time hoping that the PC will maintain the integrity of enough system files to keep itself alive, which isn't really a sensible way to spend your evening.
Basically, you have a number of expensive paperweights that should be isolated to keep the infection from spreading any further and then reformatted and the various OS's reinstalled. No files with either the .exe or .scr extension can be backed-up due to the potential for reinfection of your machines once you put them back.
If you try to remove the slime and miss just one file, you get the infection back again and in a networked environment you just multiply the issue. Sorry that it's not better news, but that's just how it is.