Google the following:
MPEG Streamclip
VLC Player
Then hit up the following pages at the WoW Wiki:
http://www.wowwiki.com/Mac_Video_Recording_and_Editing
http://www.wowwiki.com/Mac
Now, if you have a problem like the one above, I advice googling something like "wmv iMovie" or "how to get wmv to work in iMovie".
I'm not trying to be condescending, just trying to help you help yourself in the future.
Another thing you can do is to start hitting up the websites of the major producers of WoW Machinima. I know at least one or two of the biggest names around do their work on Macs. Baron Soosdon maybe?