I stumbled across a method of converting unprotected wma files to aiff files using free tools you probably already have.
If you have iMovie HD 6 and Flip4Mac, then you can drag a wma into an iMovie project and it and Flip4Mac will convert the file to an aiff. You can find it within the media folder in the movie project.
You can then let iTunes convert the aiff to the compressed format of your choice. Since you're going through a double conversion, I'm assuming there will be some loss of quality. I couldn't tell the difference in the stuff I did, but your ear may be more demanding.
The best free method of converting WMA audio is to use MPEG Streamclip. You might need the free version of flip for mac installed as well (as MPEG streamclip uses quicktime). When opening WMA from the file menu you have to select 'all files' from the dialogue box to open them. Then all you do is select 'Export Audio' and the file can be converted into ipod friendly AAC (M4a) audio. The reason this app is the king at this, is because you can batch process files from the 'list' menu (batch list). Very efficient and free!