Just want to report in with this one in case anyone else has had problems with it.
It tried to launch when I booted up this evening and Avast! spotted it at once but couldn't delete. After several attempts at scanning and trying the various options of Repair, Move to Chest etc I scanned in Safe Mode with System Restore turned off and Avast then managed to delete it properly.
I've run more scans after rebooting in normal mode to ensure that the file really has been fixed, which it has - it was in My Documents and trying to launch from there as the system booted up my folders into the virtual memory, which was why the alarm went off.
You guys rock, I wouldn't have known how to do any of this if it hadn't been for all your help:)
Just wanted to reassure people that scanning in Safe Mode and deleting the infected file via Avast with the delete on next bootup option checked seems to have worked with this particular virus, however I do not know what would have happened had it got into my System files. I'd probably have had to delete the file manually.