I use Flip4Mac CONSTANTLY. What a life/business saver!
Player simply plays back WMV in Quicktime.
Player Pro allows you to edit WMV files in programs like iMovie or FCP. It also allows you to open the WMV in Quicktime and simply save it as a MOV file. I find that the easiest for editing.
Studio includes Player Pro and allows you to export WMV from iMovie, QuicktimePro, FCP, Compressor2.
Studio Pro includes 2 Pass encoding for better quality bit rate targeting and includes Player Pro.