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.