Michael added a 2TB drive into his old Windows XP machine and installed Windows 7 on it. Now his computer won't boot to the drive with Windows 7 on it. Leo says he'll need to tell the computer that the Windows 7 drive is the boot drive. When he boots to XP, though, he can't see all of his hard drives. Leo says it could be that the hard drive is too big and XP can't see it.
Leo suggests just switching the drives around, so the new drive is plugged into the same connector the old drive was. He can also switch the boot order in the BIOS. He now has a dual boot machine with Windows XP and Windows 7. Windows 7 Pro actually has Windows XP emulation as well, so he could just use that instead of switching to the XP install. Leo recommends not using Windows XP online after April 8, which is when Microsoft will stop supporting it with security fixes.