There are a few of issues here that may help you to clean this machine.
First. Did you download the Symantec tool onto a clean machine? When a virus like this is active, there is no telling what it is getting up to and it essential you download onto a verified clean floppy and then write protect it. The only way you can be sure of this, is to use an un-infected machine.
Second. Did you boot his machine into safe mode and disable system restore BEFORE trying to clean it? There is a known issue regarding this, and I believe it is the only way to eradicate this virus.
Third. If you read the Symantec site, there is an option to stop the virus with a registry hack and deletion of the primary executable file (MSBLAST.exe). This option does work, (I've used it) and then gives you the option to run up to date anti-virus software to clean out any remnants.