Throttle down CPU speed of VMWare image

This VMware guide on virtual to physical machine migrations should be a good start, though it looks like you're required to use 3rd party tools like Sysprep and Symantec Ghost.

PlateSpin makes a commercial tool called PowerConvert that does both Physical-to-Virtual and Virtual-to-Physical conversions.

I have seen this behaviour when I assign too much memory to the VM's. When I start a VM that grabs memory from the host OS above some threshold, everything dies except for the hard drive LED. It takes an age just to shut down the VM.

Fine-tuning the memory footprint of the VM's has done wonders for me.