Use export>Quicktime conversion
I have Flip4mac on my Final Cut 6 system and wmv shows up as an option in Export Using QuickTime conversion. The pathway is File> Export>Using QuickTime Conversion. When you get the save window, click on the Format list and .wmv should appear along with the other output format choices. If you want to customize the .wmv file, click on the options button and you can change the settings, size, etc. If you don't want to customize, just click on save.
Good luck.