DO NOT attempt to access your Tivo HD with Windows. Doing so could leave your Tivo drive unreadable. If you want to back the image up to your Windows drive use MFSTools which can be found on this site. After you have the image you can burn it to a CD if it will fit. My image backup was 1.5 GB.
Additionally, the backup process is done in a Linux shell. You will boot off your CD ROM drive with the MFSTools disc. Read the MFSTools thread for instructions. You may want to reinstall your Tivo drive into your Tivo to verify that it still works. If not, I do not know what to tell you to do. However, there are those on this site who most likely can help you.
Good luck.
Additionally, the backup process is done in a Linux shell. You will boot off your CD ROM drive with the MFSTools disc. Read the MFSTools thread for instructions. You may want to reinstall your Tivo drive into your Tivo to verify that it still works. If not, I do not know what to tell you to do. However, there are those on this site who most likely can help you.
Good luck.