The only reason Norton is failing to clear the problem on this PC is because the detection of the infection is being done when Windows has been booted normally - the files are locked by the OS so of course they can't be cleared.
Any software would have run into the same problem clearing this infection.
Just mentioning this to dispell the usual BS about Norton being "rubbish".
But hay - it's like telling people to stop saying M$, Micro$oft and bashing AOL.
It appears to be the fashion to do so even by the uneducated...
I think it is safe to say that at some stage this machine has been online without any AV software running or outdated definitions.
Either prior to Norton being installed or due to it being turned off by the user so that they can get those important 10 or so more 3DMarks (or similar) as Norton's constant checking (as all AV software does) would have detected the infection as it was coming in.
The key to removal these days is doing the full scans in safe mode as this is the only way you can be sure that the infected files won't be locked by the OS.
System restore should also be turned off - however I would recommend you do not do this until you are sure that your machine is clean.
It maybe that using System Restore is the only way to get your machine back into operation and switching System Restore off will delete all of your restore points.