My friend wanted to upgrade my computer, so he installed a pre-market version of windows7, that has expired already . I want to remove it from my PC. I am very Happy with the XP Pro Instalation that is already up and running just fine.Please Help me to get the 7 OFF of my PC!!!!!

Install EasyBCD from http://neosmart.net/dl.php?id=1 and use that to reinstall the XP bootloader. Then format the Windows 7 partition, after recovering any information you may need. The hard way is explained at http://support.microsoft.com/kb/314058. You would need the fixmbr command.