You must first remove all traces of your previous XAMPP installation before trying to install a new version.
Did you follow either of the 2 uninstall instruction methods
in the XAMPP for Windows home page?
Or in the http://www.apachefriends.org/winxampp/readme_en-lite.txt
If the old 1.7.2 folder won't delete then either a service or a file is still being used by Windows and may be the reason you are having trouble with installing xampplite in to the proper default location.
Perhaps disabling the UAC temporarily may help:
To disable UAC
go toStart>Control Panel>User Accounts
there you will find an optionTurn User Account Control on or off
just click on it and uncheckUser Account Control to help protect your computer
You may also consider becoming a Super Administrator
that may give you more control of your PC.
Before you try and remove 1.7.1 lite, which you should to get a fresh start, make sure there are no ticks in the Svc boxes in your XAMPP control Panel.
Make sure all components are stopped and the XCP is closed.
You should now be able to remove the 1.7.1 folder.
Next reboot and try and remove the original XAMPP 1.7.2 folder again.
Post back if you get this far as we may be able to get rid of the MySQL NT Service, that is giving issues, from the registry.