For whatever reason, vmWare Windows systems sometimes randomly spin out of control consuming 100% of my CPU. The solution is simple, open up a Task Manager in each Windows virtual machine until you find a process named vmwareuser.exe that is consuming 100% of the CPU. Right-click and kill the process. I have no idea what the process is for, but killing it does not affect the apparent stability of the virtual machine (in fact, my opinion would be that it increases stability as it drops my processor consumption from 100% to less than 10%).
There are a number of threads on vmware.com's forums about this issue, though nobody seems to have any good answers as to the cause or a patch: