If you installed the paid version of Flip4Mac, all QuickTime apps will be able to load WMV files. Except, alas for Compressor, which does very annoying filename filtering against formats QuickTime can read just fine, like WAV. However, you can load the WMV in QuickTime, do a Save As to a .mov (which doesn't recompress), and then load it into Compressor just fine.
Goofy, but it works. Tools like Adobe Encore can load WMV straight onto the timeline, which is nice.