Keep in mind that some virus damage is so deep
That you have to get the user's files out then start over. An example is that recent ZeroAccess Rootkit. Here's the discussion -> http://forums.cnet.com/7723-6132_102-578886/zeroaccess-rootkit-symptoms-found/?tag=contentBody;threadListing
While I know how to fix that one it required the Microsoft issued OS DVD and a paid version of an antivirus of a specific company. The owner in one case could never get said DVD and in the next case they decided to start over.
Until we know the name of the pest, removal or writing much else is a dead end. Until the name is known, prepare for a reinstall of the OS.