Well done.
I felt the same about trying to remave a dual boot and how there is little information on what Vista will allow you to do after installing a dual boot config.

I installed the Vista trial, to see if my programs would have any issues. After I determined everything was working and wanted to remove XP I learned the hard way , same as you , on trying to remove XP.

I hope we helped, or at least let you know that it is possible.