You're on the wrong forum for questions like this really.
Check out this thread on the same topic that I started on Cinema5D.com:
http://www.cinema5d.com/viewtopic.php?f=13&t=11475
I managed to do the conversion with Quicktime pro (exporting as individual images, then importing), but other people had better suggestions including
Jes Deinterlacer and a Python script which just updates the file to change the playback frame rate setting.
Whatever you do, don't use iMovie. iMovie will conform your clip down to 30p or 25p on import (by chucking the extra frames away) and will then slow it by just replaying those frames less frequently. You end up with a jerky result, and you've undermined the whole point of shooting double-cranked at 60fps in the first place.