It depends on if you mean "TiVo", or something "TiVo-like". TiVo is not available on your computer, but several products like it are.
If you have a PC, there is software that will give it the ability to act like a TiVo, and record television programs. However, that PC will need a television tuner card in it.
Assuming you do have a television tuner card, there are two solutions that immediately come to mind. First is Microsoft Windows Media Center. It's a version of Microsoft Windows XP with all the TiVo functionality. However, you can only get it with the purchase of new hardware (Like a TV tuner card or a new PC)
The other solution is MythTV. MythTV is an open source PVR (Personal Video Recorder) project, which you can get at http://www.mythtv.org/
It works with many tuner cards, and assuming you have a decent hard disk, provides a lot of TiVo like funcationality, including recording your favorite shows.