OK, I dual booted by accident! I tried to install Vista Premium Upgrade and found (like many others) that the Upgrade option is not available. So, I did the Custom install and loaded Vista onto the spare drive (drive d and initially got an error code. I thought that I was in trouble because this was an Upgrade disk and didn't know if the install would take. But after about another 20 minutes, I've got a computer with XP on the C drive and Vista on the D drive with the option to choose at boot-up.
