Look in the DirecTV Tivo Hacking Forum in the How Tos Only sticky. There must be at least three or four different tutorials on making a Tivo serial cable. When in doubt, read the sticky threads for pertinent info. These forums originally centered around DirecTivo hacking and the development and implementation of 2.5Xtreme. SA Tivo support was added later. Any instructional info will almost always be contained in one of the sticky threads so look there first.
Please don't PM me or any other members looking for personal assistance. You'll do better by posting (after you've exhausted the search feature, of course) and taking advantage of the collective expertise of the membership instead of a single individual that may or may not be able to help you. Thank you and enjoy your stay at DDB!