According to MS KB 957006 ( http://support.microsoft.com/?kbid=957006 ), MOSS 2007 SP1 and WSS 3.0 SP1 are supported in the following virtual environments:
Windows Server 2008 and later with Hyper-V
Microsoft Hyper-V Server 2008 and later
Server Virtualization Validation Program (SVVP)
Support policy for non-Microsoft virtualization platforms (such as VMware) is posted in KB 897615: http://support.microsoft.com/kb/897615
For recommendations on optimizing virtual server performance, see this article:
http://blogs.msdn.com/uksharepoint/archive/2009/03/04/topic-1-recommendations-for-optimizing-the-performance-of-a-virtualized-sharepoint-environment.aspx
Generally speaking, minimum software and hardware requirements for virtual installations of SharePoint are the same as those for physical servers (see this Technet article for details: http://technet.microsoft.com/en-us/library/cc262485.aspx). If your systems meet these requirements but the performance results are still unsatisfactory, I'd suggest contacting VMware technical support and ask them to check your VMX configuration.
Andre Galitsky, MCTS, Lexington, KY -- My SharePoint Blog: http://www.sharepointnomad.com