round-a-bout way, but all i can think of off the top of my head...export from Quicktime as .mov, import to iMovie, use special effect (video effect) Slow, Fast, Reverse, to slow it, re-export.
If you just want to play it slower, the QT player allows you set the frame rate for play. QTPro will allow you to save the file as a QT movie with the changed frame rate (I don't think the free player allows you to save a new frame rate).
If you have QTPro you might try what the other guys are suggesting, but to answer your question:
Drag your clip to the timeline area, Then below the clip selection area, go to Editing, Then above the selection window, near the top, select Video Effects, and then look through the effects, Fast, Slow, Reverse is one of the choices.