I asked Ben over at "Virtual PC Guy" blog about some tips for tweaking my VPC performance.
Specifically i was curious about the speed difference between virtual IDE and SCSI drives. He said that with the VM additions installed, virtual SCSI drives will perform better.
Also, he said that fixed disks are going to perform better than dynamically expanding disks. When setting up my VPCs from sysgen-ed templates, I'd been using dynamically expanding disks to keep the .vhd file sizes down. I just turned off my VPCs, and converted the .vhds to fixed, and re-linked them to the VPC. Took about a 1/2 hr or more, but it should be worth it.
I read on MSFT.com that defragging the host computer drive will help alot also, so that's one last thing i'm doing before tying off all the loose ends on this host machine, and getting down to some real dev work.