A quick google search for "wma to mp3 converters" reveals a bunch of promising hits. You should be able to find a free program to convert your current wma files.
I think that you can change the format that Windows Media Player automatically uses when it rips cds, but I'm not sure, as I haven't used windows for that in a while. I know that the default ripping format of iTunes is mp3, so that is another option.
-Tom