You are sure you are logged into Vista as an administrator?
Reboot your PC and make sure you log in as an administrator and see if you can delete the xampp folder - let me know before moving on to the reinstall if the folder has gone.
Is there not an uninstall file that is part of XAMPP when you use the installer version?
(I only use the EXE (7zip) version as I personally don't like installers
Make sure your virus scanner is not blocking the delete by temporarily disabling it, then try and delete again.
You may have a file that is still in use in the folder which will prevent the folder from being deleted.
Also check the permissions set for the folder by right clicking on the folder Properties>Security edit the permission to give you the admin full rights.
Here is a link that has some fixes for this deleting issue:http://forums.techguy.org/windows-vista ... d-you.html
Here is a link to the Secret Super Administrator setup (very easy):http://www.winvistaclub.com/t12.html
If you use the EXE (7zip) version it is self extracting and no need for zip software and in my opinion is much more reliable and just as easy if not more so than the installer version.
Download and extract to the C:\ drive and it will put all the files in C:\xampp (after your old one has been deleted).
Then run setup_xampp.bat file to set all the paths correctly.
Next open the XCP - xampp\xampp-control.exe - and start Apache and MySQL.
Then go to http://localhost/
and select you language and you should be taken to the Welcome Page.
If all is well you should be able to go forward.