I have just installed ESX 3.5 in worksattion 6.5. I then installed another vm in workstation running win2003 and SQL then just for the hell of it installed win2003 and virtual centre in the vm running ESX 3.5 and it works!!! All this is running on a packard bell laptop with 4 Gb of ram and dual core amd athlon 64 bit. The amazing thing is its perfectly usable. It took a bit of vmx file editing but it works none the less Edit
It's cool isn't it. After I did my fast track course on 3.5 I knocked up a training envirnment is WS 6.5. 2 ESX hosts, Openfiler iSCSI SAN for shared storage and VC running in WS VM's. I was able to build a VM within the VM ESX server, install 2k3 on it then vmotion it between betwen the 2 hosts. Ran all this on my Dell Precsision M6300 with 4 GB RAM. It was slow but I could work through all the courses labs quite easily on this training rig.