Just a quick tip – I noticed lately that whenever I fire up a VM on my machine, ALL four processors would shoot up to 90+% utilization. In addition, the VM (typically running Vista) would take a good 10-15 minutes to load (okay, a bit of an exaggeration – but it took forever.) 
Took me a couple of minutes to figure out that it was my anti-virus software that was causing the issue.
As I mentioned before in a previous post, I’ve installed ClamXav software on my Macs because of the rising popularity of Macs (this begets challenges to hackers which begets to virus being written for OSX, etc. — or is that just my paranoia?) The program installs easily enough and updates itself regularly etc.
If you are using ClamXav Sentry and VMWare, you MUST exclude any VM images from being scanned! Better yet, make sure that you configure your ClamXav Sentry to ignore scanning the directory in which you keep your VM images. This will dramatically increase the start time of any VM. If you opt for the extension method of exclusion, VMs have an extension of .vmwarevm .
-JT