I have a client who is running SQL Server 2005 Standard Edition on a VMWare ESX operating system. I wondered if Microsoft supported this environment and did some digging. I had some difficulty finding current information, so once I found it, I thought I'd share it with you.
As of November 2007, Microsoft says they do not support third party software virtualization. They require that you reproduce the issue in a non-virtualized environment before they will help you. Here's the link confirming that: