Sorry it isn't working out for you. As for your specific question, go to the url shown below. Download and burn slowly the latest stable version of the SuperGrub live cd iso.
You can use this live cd to re-install the Windows pointer to the MBR. This should put your internal hard drive back as it was with the Windows boot loader.
If you want to get rid of the Linux partitions on the external hard drive, use the Mint or Ubuntu live cd. Open gparted from the menu and delete the partitions on your external drive. You can then create one or more NTFS partitions on the external drive that Windows XP can use.http://developer.berlios.de/project/sho ... p_id=10921
The iso you want is at the bottom of the page.