multiple VMs

Linbox

I didn't realise that VM player needs to be restarted from the main start menu if you have a vm running, it will then quite happily run another vm. I prefer vmplayer as I found you can just copy a vm from explorer as a backup.

Ximian

Have a look into snapshots if you test/install on any of your VM's, instead of having copies of VM's you can take a snapshot before you install or modify the VM and roll back to a previous state if you want. VMware Player doesn't support snapshots though, VMware Server (free) does as well as Virtual Box

RussJK

Good point about snapshots, saves a lot of hassles especially for before/after testing.