Do you mean the system32 directory? There're lots of files in there, most likely your only option is to install windows over it.
Some information on the worm:
http://vil.nai.com/vil/content/v_99881.htm
From the description, seems like it's targeted at kazaa users... from MPAA/RIAA?
Since that worm doesn't infect any file outside the kazaa download directory, it's possible that something else deleted yours system32. Update your mcafee with the latest definition and scan your whole computer again. Some viruses disguise themselves as "system32.exe" so that could be a problem as well.