If this is a stupid question, I apologize in advance. But having done a rough edit in imovie9, am I now committed to staying within mac editing software? Or is there a way to convert .mov files to something Vegas could recognize without losing any quality?

I don't know about iMovie .movs. I think they're different than FCP .mov files. What you can do, however, is download (for free) Mpeg Streamclip, then use it to convert the files to .avi.

iMovie transcodes video to the Apple Intermediate Codec, AIC for short. Unfortunately the AIC playback is not available for Windows, so you'll have to transcode the video one more time to get it to playback on a Windows PC. Your best bet is to re-import your video on a PC, preferably using Sony Vegas.

But you will lose the edits you made in iMovie, I have not come across any successful way to translate edits to Vegas, except for very simple one track edits. ** I have successfully, made edits in iMovie, and then transferred the edits to FCP, which then went to Premiere on the PC, but I was careful to start with a video file format that was cross-platform compatible, in my case Cineform.

One more bad thing, if your original was 1080p / i, iMovie renders its own file @ 960x540, so anything that comes out of imovie is permanently degraded by half.
But, you can save your project file and open it up in FCP, as long as FCP has access to the source footage, you could export dnxhd, or animation if you have enough space, and then put it on a PC and have a lossless transition between platforms.

I'm working with footage shot on the older Sony HC-3 but I imported it at the "full size" 1920x1080 (rather than "large size"). So I"m going to be burned in the export process no matter what I do, whether I convert files for PC consumption or whether I import into FCP (which I'd obviously rather not do)?

interesting for me, thanks