Don't you love the User Account Control(UAC) now seen in Vista like a over glorified firewall. That's a fast trip into the control panel>user account to see that unchecked!
As for what happened when installing a newer version of Windows? It replaced by compression the older version. The new Windows sees the "users" folder in place of the DocumentsandSettings. If you try opening the new copy by the same name you will get the access denied error.
How to wipe it all out? The Vista installer has that ability to delete the current primary. A preferred 3rd party drive tool used by many however is the live for cd GParted a free Linux tool that can also create, delete, resize, even copy MS partitions. That remove any primaries whether Vista, XP, Linux, etc. with ease.
The 0.3.3.0 release was the last for being "platform independent" however found at
http://sourceforge.net/project/showfiles.php?group_id=115843&package_id=173828
For general instructions with screenshots,
http://gparted.sourceforge.net/larry/generalities/gparted.htm
You will have to scroll down about 15 versions on the download to find the 0.3.3.0 and also 0.3.2.0 releases with the later being older and a little slower loading.
If you install XP Pro64 with the Vista drive plugged in you will that as the D drive with in XP. And if you plan a dual boot remember when loading XP all of Vista's system restore points are canceled out. I'm currently beta testing a prebeta tool that sees that problem taken care of soon to be in the beta #1 form for more then a few select users.
