Hi, Just thought I'd pass this comment on to folks in hopes of saving some time. In order to run 64 Bit OS's under VMWorkstation (either 32 or 64 Bit) your processor, BIOS, Motherboard, etc. has to support both EM64T and VT. VT standard for Virtualization Technology. It's code name was Vanderpool. I believe it's a newer name than EM64T. The following is my experience on an ASUS P5E-VM HDMI motherboard with 8 Gig of Memory and AMI BIOS 0604. I'm running Vista x64 SP1 as the base OS (I.e. VMWorkstation is running in this OS). I was able to duplicate the results with Vista x32 as the base OS. VMWorkstation was capable of running 64 Bit Apps (I.e. ESXi 3.5) when using an Intel E6600 (dual core) Processor. However, VMWorkstation was not capable of running 64 Bit Apps (again ESXi) when using an Intel Q8200 (quad core) processor. Intel shows both processors supporting EM64T. However, I believe only the E6600 supports VT. There are no specific settings referring to EM64T, VT or Vanderpool in the latest AMI BIOS ver 0604 for the motherboard. All BIOS settings were default. The problem I was encountering "followed the CPU" when I switched the CPU's between two PCs, thus I'm pretty sure its the CPU.
Anyway, the error In VMWorkstation that I was getting with the Q8200 was "This host is not capable of hardware virtualization, using software virtualization instead". The Software Virtualization was so slow that I could barely log into the VM once it "finally" loaded. It was quite "Zippy" with the E6600 CPU. VMware has a utility that checks for compatibility at http://www.vmware.com/download/ws/drivers_tools.html. This utility doesn't need VMware to run.
I think the above is all correct (ASUS hasn't gotten back to me) and I hope I save someone else from buying the wrong processor for VMWorkstation if they intend to load 64 bit VMs. The only other thing I can think of is that the BIOS on both of my Motherboards doesn't set up EM64T VT on the Quad processor correctly. I haven't found anything on the INTEL or ASUS sites about this.
Just as an added curiosity, I was able to run ESXi 3.5 natively on the ASUS P5E VM HDMI motherboard with the Q8200 processor as long as I added an Intel Enet card (PCI Pro/1000 GT Adapter) that uses the e1000 device driver. (My home playground machine for learning).