Hi wrm,
How many virtual processor cores have you assigned to the virtual machine?
Could you go into your virtual machine's Settings> Advanced, and set Troubleshooting to Crash/Hang, then attempt to reproduce the problem again? Maybe the resulting vmware.log will have a hint as to what's going wrong there.
It's been a long time since I last used Gentoo... that Prefix project looks quite interesting. 
Cheers,
--
Darius