sorry man why don't you convert your songs to mp3? it may be not too easy, but i think this way it should work: convert them to wav using for example winamp, and then convert them to mp3 with any mp3 conversion program.
nullsoft should add the feature that enables winamp to scan inside zipped files and play the files right from the zip(/rar/...)-archive. i have lots of big zip-files with modules in it. it would be cool if i wouldn't have to extract them every time.