I know on the PC side, there are several shareware and freeware apps that do the conversion of WMA to MP3... But a quick search on VersionTracker didn't yield any for the Mac... Will continue looking...
"Can anyone tell me how to rip a WMA file and convert it to a MP3 file?"
I poked around the 'net looking for a tool that would convert a WMA file to a WAVE or AIFF file (since it's pretty easy to convert either to an MP3 file) with no luck. There don't even seem to be any tools for Linux that are able to decode a WMA file.
There is a Windows Media player for the Mac; maybe that will let you convert WMA files to WAVE/AIFF files?