Windows 7 does not use boot.ini. You could repair the boot parameters using one of a number of boot utilities but probably the easiest way for you to sort this would be to reformat the drive with Win 7 on it, boot from the XP with the Win 7 drive installed, repair the XP install and install Windows 7 to the new drive under XP. This will set the boot options on your XP drive to select either system at startup.