A quick look at viruslist.com and I see it's a nasty type of virus.. files everywhere..
http://www.viruslist.com/eng/viruslist.html?id=1666084
Because you may be dealing with ntfs partitions, you can't rely on GPL tools.
I suggest you make a clean XP machine, install an antivirus programme that can clean mailbox/pst files and clean each hard drive in turn in the clean XP machine. After a while you will have 2 clean machines to check with, then 4, then 8 etc
You can't afford to have a pc start before being cleaned unfortunately..
After each one is cleaned, make a boot disk that will remove the registry entries and consider installing antivirus software everywhere, esp the mail server.
Force ALL mail traffic through a mail server that will check/clean everything.
Unfortunately, you now are part of the world wide problem of spreading viruses from your network, so anything you can do to stop them leaving is a step in the right direction.
I hope you get some sleep over the next few days. Good luck.