Microsoft Windows Server 2008 X64 on VMware ESX is now possible as ESX 3.5 Update 2 has been certified as seen here. This also means that you can install Exchange 2007 SP1 x64 in there too.
I saw this on BrettJo’s Exchange Blog..
Cloudy with a chance of Licensing
Latest news on Microsoft licensing, Cloud, and AI
Cloudy with a chance of Licensing 