Yes, ZipPSW worm is a kind of heuristic for detection of password-protected attachments of some (mostly Beagle) worms.
So, it is a password-protected ZIP having an executable file inside. It is possible that it's a false alarm. In any case, you don't have to be worried much about it; even if it really is the virus attachment and if you open it (entering the correct password), the Standard Shield would not let you execute it.
What exactly do you mean by "cant seem to clean it"?