Smitfraud

Please help!  Neither my husband nor I are really tech savvy and his Dimension 2400 has caught that Smitfraud virus.  I've tried to start from Emergency disks, from the original set-up disk that came with the computer, and from Norton Systemworks as an emergency CD.  Nothing works!  It goes as far as the Windows "welcome" screen, then freezes.  It will not respond to "Cntrl+Alt+Del".  The only way we can try to restart it is by shutting off the power, then turning it back on.  I've run the anti-virus part of Norton Systemworks from the CD and it says that it has scanned and found no viruses.  It also says that it will not scan compressed files unless we define the parameters or something.  I have no clue how to do that!  Does anyone have any ideas how I can progress beyond the welcome screen to try to isolate the virus and get rid of it?  By the way...he uses this for his business and has not backed up his files.  I am fairly certain that I can salvage his data from QuickBooks if I can get past the welcome screen (or I could even save the data to a jump drive, then reformat his hard drive if necessary).  This is why I don't want to just reformat the hard drive.  If I can get to System Restore, will it delete his data?  Thanks in advance for your help.--Mamadog531