I, also, advise against windows media player...can actually cause conflicts on your mac.
I haven't used the easy wma thing, but it sounds like it's for audio, and may not do video. Maybe there's an "easy wmv" version.
If not, try
Flip4Mac, but to convert stuff with that, you have to pay for the upgraded version. If you do that sort of thing often, it's worth it.
There's a site which says it will convert formats of video
HERE. Might work for you.