http://www.nch.com.au/switch/

Dave, download this programme, it's freeware and out of all the MP3 converters I have tried I reckon it to be the best so far. It does pretty much ALL the file types, to and from, and is about the quickets too

And it will certainly convert WMA to MP3 and vice versa

Oh, and it does the whole track not just the first 75%