The beta 2 of VMware Workstation will contain a permanent fix for this problem but until then you can start a Virtual Machine running in ESX 3.5 hosted on Workstation 6.5. The only thing you have to do is minimize the resources.
From the ESX or VC client, highlight the VM and select > Edit virtual machine settings
Select Resources tab
Un-check Unlimited in the right pane and lower Mhz count to 700
Select Advanced CPU in the left pane
Under Scheduling Affinity in the right pane > Select Run on processor(s):
Check "0"
Click OK to close VM edit window
Boot VM
I'll say this much - this isn't a great fix. Although it does allow for additional testing, VM performance is dismal at a minimum. I'm going to play with MHz and Affinity settings to see if I can get better results.
