I'm not sure what physical size your TiBook's drive is, but you looking for something that's ATA and is 128GB or under. (because the IDE controller can't see anything larger).
Once you find out what size your drive is (2.5' or 3.5' perhaps) then you're golden. Finding a replacment on eBay should be easy.
Keep in mind searching for the actual specs of a drive will yield more results then searching for a computer model. You should also find better prices.