First, you probably need to find a new antivirus provider, and make sure that your email server has virus protection on it. Most networks don't get repeatedly infected like that.

Second, you need to lock the machines down so that users are running on standard user accounts without access to install software. This will help cut down on the amount of stuff that can get through.

Third, the easiest way to deal with these scenarios is to start using System Images for the PCs, with a software package similar to Ghost. This way you build a single image and can easily re-deploy to PCs, wiping them clean of any crap on them.

To make that strategy succeed, you'll need to migrate user data from the desktops to the servers instead, so they aren't wiped when the PC is reloaded. You can do that with roaming profiles and exchange server, or just turning your PCs into thin clients with a Citrix environment.

These aren't the only answers, and I'm sure the other guys will contribute - this is just the strategy I've used in the past.

Very nice post, Kevin.

In my experience, servers very rarely chew up a lot of CPU unless they are very heavily utilized, and RAM isn't an issue when dealing with ESX server on a powerful box - we've always been able to run a ton of VMs at once, even with a lot of activity on each.

The performance issue almost always comes down to disk access - we would have SQL Server boxes returning results in 10x the time they should have because so many of the applications were reading from the disk (internal RAID array) at once.

Moving everything to a SAN and keeping the worst offenders segmented helped make everything run smoothly across the board.