I haven't used an HF200 (I'd like one). It looks like it is compatible with iMovie 09.
See their list.
iMovie 09 will import the MTS files
from the camera to a format that iMovie can handle for real time editing. You then upload your project either via an iMovie option, or by exporting the project and uploading it via YT's web interface.
I don't see anywhere
on the YouTube help page where MTS is a supported format.
Here is the short story for using iMovie 09.
1.) record to the camera (in its native format).
2.) connect the camera to your Mac.
3.) startup iMovie (editor) and choose the import from camera option. Clips appear in Events.
4.) Create a project..
5.) Drag content from Events to your project.
6.) Fine tune, add effects, transitions, extra audio, etc.
7.) Export for public showing.
Apple has tutorials online via the iLife page that shows you how this should all work.