Spurred on by this thread, I have tried vmware, MSVPC2007, and VirtualBox. My main reason was to look for a reasonably stable virtualization environment initially for my main desktop machine but ultimately to consolidate some of my server HW (all home stuff but it is starting to add up). I tested them with CentOS4.5 only though and on a host of Windows XP Home.
All running on Core2 duo 6600 on a high end ASUS Mo Bo and 3GB RAM.
My off the cuff thoughts:
VMWare Server 1.04: Stable, broad support, but the free version at least is slow and poky. Aside from somewhat sluggish response, the audio card stuttered (no matter what mods I did). In my opinion, VMWare 1.04 was barely usable due to the sluggishness.
MS VPC 2007: though officially not support on XP Home it did intall and worked reasonably well. I couldn't get the Tools to install on the guest OS as they all seem to be geared to MS guests only (surprise surprise). For whatever reason with CentOS as guest, it could not see the audio card at all. The other issue was it is 16-bit colour support only so when I installed CentOS (which defaults to 24-bit), the display went haywire. I corrected this by installing CentOS with 16-bit colour option instead. Overall this worked quite well though I wish I could get Audio to work.
VirtualBox 1.5.2: it was a little unstable and crashed intially (but it has stopped doing that). I had to boot CentOS as non-SMP otherwise it hung decompressing the kernel. Other than that it runs quickly and the audio works (as well as other devices). I did have some weird issues with PGP keys on some rpms when I was doing a yum install of vlc. All other VMs had no issues. it is hard to imagine what the VM could have done to affect this but you never know; I chalk it up to bad timing from the repository.
So in conclusion, I will not continue with VMWare unless I find a compelling need for it. The other two I will continue to play with to see how well they work through other scenarios. But at least VirtualBox should be able to run with SME as it's Host OS (in theory).
I hope this helps someone.
I would be curious of other people's experiences.
Christian