Flip4Mac Player Pro ($29) http://www.telestream.net/flip4mac-wmv/wmv-player-pro.htm
Allows you to use WMV directly (performs sluggish in FCP)
Allows you to wrap WMV in MOV (preforms a bit better in FCP)
Allows you to re-encode WMV to whatever codec you need/have installed in QuickTime Pro. Becomes whatever you make it but involved a re-encode.