A month or so ago I purchased a 1st generation, DiY TiVo. It is a refurbed unit that is missing its hard drive, I figure for 15.00 (+ shipping) what could go wrong? quite a bit actually.
Firstly, you have to format your new hard drive so the unit will understand what in the heck you want it to do. After searching the web for instructions on a fresh install, I gave up and purchased a program called InstantCake. To use it, you have to use a PC, move your CD/DVD ROM (by itself) to the primary slave position, and the drive(s) you want to bake in the secondary IDE master (slave) position. They suggest disconnecting any other drive not associated with this process.
The hard drive I originally selected was a Western Digital 320GB Caviar Blue... that was a mistake,
Do not try and use this drive for an upgrade, it will not work, they don't play nice with the TiVo and will not boot. Luckily I had an extra 120GB Seagate laying around which will give me up to 120 hours of recording.
Overall, the complete system ran less than 150.00 (including the hard drive that Im using in a backup PC instead)
UPDATE: I had to make one more trip to Best Buy and grab a $10.99 cable splitter, mainly because the HD channels couldnt be tuned in using the TiVo, the TiVo is using the s-cable input on the TV now.