Since switching to Vista I've nothing but headaches when I try to run some of my VPCs.  I kept getting an error saying that the virtual machine can't be started because it was being used by another program or was read-only. I know for a fact that it's not being used by another program, nor is it marked as read-only. 

The files are marked as Read / Execute for my ID, and not Full Control as one would expect. So, the error message is somewhat true.  The file is read-only to my account.  Just not the read-only we would normally think of.  To make this VPC work, you'll need to do 1 of 2 things.  Either change the permissions on all of your VPCs or run VPC as Administrator. If you set VPC to run as admin you're going to be harassed by that UAC prompt every time you run it.  So the easier solution is to change the permissions on the folder that contains all your VPCs.  Just right-click on the folder that contains your images, and select Properties.  Then click the Security tab and click Edit.  Highlight Users and then click on Full Control. Click OK and work your way back out of the menu.  The permissions should propagate down to all the files and folders under the one you changed. So be careful about what folder you change the permissions on.

Now you're ready to enjoy the virtual world once again!