64 Mb image on VMWare hypervisor. And you're being irresponsible for not running AV on all Windows servers -- the same logic that people use when they state the need to run AV on UNIX servers -- to keep the Windows machines from getting infected.
Windows machines don't get magically infected by viruses via pixie dust. A virus, by definition, requires the user to run an infected binary under a sufficiently privileged account for the payload to execute and start infecting other binaries. I would hope you do not run random binaries on your servers, whether Windows or Unix.
Exploits are a different thing, but a successful exploit will generally not be detected (and certainly will not be prevented at the moment it happens) by AV.