Run this on the system:

[link|http://housecall.trendmicro.com/|http://housecall.trendmicro.com/]

See if it turns up anything.

If Windows is majorly infected, try this Ultimate Boot CD and run a DOS scanner on the hard drive:
[link|http://www.ultimatebootcd.com/|http://www.ultimatebootcd.com/]

Of course a safer way is to make a modifed Knoppix Boot CD with F-Prot AntiVirus on it:
[link|http://www.cs.bsu.edu/homepages/gjjones/administrivia/stories/2003/06/24/fprotVirusScanningWithAModifiedKnoppixCd.html|http://www.cs.bsu.ed...iedKnoppixCd.html]

If it has NTFS neither of those two CDs will clean the virus(es), create a BartPE disk to clean NTFS hard drives using McAfee AV on it using PE Builder:
[link|http://www.nu2.nu/pebuilder/|http://www.nu2.nu/pebuilder/]

It will require a copy of Windows XP (Home or Pro) with SP1 or 2003 Server to create the BartPE boot CD.

Another method is to mount the infected hard drive on another machine and then Virus scan it and never run anything from the infected hard drive.

Once you remove the virus out of the system, it should be safe to scrub out your email that is being sent. Do not click on the attachments and remove all emails in the Outbox folder. It might be a good idea to remove all emails in the sent folder in case one got through somehow?