Some things to think about
Theory says 5400 RPM is more than enough - and it is for general day to day - however it is nearly impossible to buy 5400 drives now.
Also when buying most of the 7200RPM drive you get an option of 8MB or 2MB cache - typically the 8MB have a 3 year warranty - definitely worth the extra $10 or so - as the drive is working 24 x7 and will almost certainly fail within the 3 years
Lastly if you start to do some of the more advanced functions the faster drives are definitely better.
I have two TIVO and have the Sanderton module for TIVO to TIVO transfers using MFS_FTP running.
I can watch a show previously recorded, have another one recording and have a third being loaded across the wire from another TIVO for later viewing - the system definitely starts to slow down at this point and the menus become sluggish - however when i had a 5400 RPM drive in my systems before they were unusable
Craig
I remember reading about why this could not be done
Maybe send a message to the OZTIVO mailing list to Darren King - i thin the Power SUpply in the TIVO does not deliver the correct/adequate voltages for a PC style motherboard - i am sure i read about this on Deal Database at some point
I have used Media Centre PCs, messed around with MYth TV and others and have never found anything as easy for the task as TIVO.
If you want all the other functions then look at adding a seperate HTPC.
Also have a look at some interesting Beta software on Deal Database - auto archive/copy content from the TIVO onto a PC and encode into WMV (i.e. MPEG4) - This would let you have a large central HTPC and use TIVO for what it does best - then get anything you want to keep onto the Central server and compressed into MPEG4 - then could be streamed anywhere around the House (other than back to the TIVO of course!!)
Craig