I suppose you're talking about watching TT replays on your computer. As a replay file is no video, rather than a small data file containing what happened during your drive, there is no other way to play it than in TT on the Playstation.
You can't. Either you get yourself a TV card/ Capture card and record the replay on your pc or the simplest way, use a camcorder and record the replay on your tv. There isn't any way you can convert the replay save to watch it on the PC. Hope this helps clear things out.