Windows 2000 viruses and security

[buksida]

A bit of a strange problem this one, we have an old fileserver running Windows 2000 Server at the office, however the software we need has been written to run with IE6 (yeah I know its a bad idea) so we can't upgrade it or install any service packs.

Now this machine has become infected and I need to find some form of security for it - Symantec AV detects and cleans the viruses but they instantly return. Two files called msudp32.exe and ms18_word.exe are the infected ones, there are probably more.

I've tried malware scanners and fix tools but these things just keep coming back through the security holes in the software. I wanted to install a firewall on it but Comodo and Zonealarm only offer XP/Vista versions.

Any suggestions would be appreciated (formatting is not an option and we cant upgrade it either as our antiquated software will not function).