Im not sure about the mac (For this I use windows) but
The PS3 can
Play HDV files natively... No need to convert to 720p..(let the PS3 use 1080i ( which is the file's native resolution) .It does a very good job with it
AFAIK
You can burn them to a DVD and play them off that, or copy to the PS3s HDD
This it can do in its media streamer mode
You can also stream them to the PS3 wirelessly or wired in thier native m2t form from your computer
Im not sure if imovie makes "avchd discs" .Nero Vision 8 ( amongsts others) can from HDV files which will playback on the PS3 in its BD player mode
Red Kawa make a converter for PS3 but it may be a windows only software hve a look at the link