Virtual SMP is an addon module, actually available only for ESX Server, that permit a VM to see more than only one CPU (only if host hardware is multiprocessor).
At today GSX Server and Workstation don’t benefit of this module nut with GSX 3.0.0 release something could change: if you carefully look at new GSX web interface you can notice a well declared “VM processors number” information. This doesn’t prove anything but I can imagine that this change is introduced for the next Virtual SMP version compatibility.
ATTENTION: No informations about next VSMP are available from VMware so this is just a speculation.