Just installed 4.0 on my alienware m15x, had to create a Snow Leopard VM, pretty simple instruction and easy to use. Runs awesome on my 3GS

Follow this, to the word

How to Install Snow leopard in VMWARE | Snow Leopard

If you get this error -

Mac OS X is not supported with software virtualization. To run Mac OS X you need a host on which VMware Fusion supports hardware virtualization

You need to enable virtulization in your system bios, works good with my system.