I have recently upgraded my home server, shelling out on a new Core 2 Duo CPU and 4GB of RAM for the machine. Having this much RAM means that in order to use it, I had to install a 64-bit O/S. I chose Ubuntu Server 8.04 - and VMware Server to host my virtual machines. I have put together a Word Document with some notes on the issues and tips I came accros on the way, which could prove invaluable to anyone taking the same approach as me. One of the main sources for my research and tinkering ideas was a post on the VMware Community forums - http://communities.vmware.com/thread/146002 - linked to within the document.
This post made extremely interesting and informative reading - if one can understand the material in that post, then a lot of load issues can be easily resolved especially IOWait issues (my particular concern). My issue turned out to be a mixture of the settings above, and Postfix misbehaving.
See the PDF here.