If you have downloaded the music using an older version of iTunes (4.x), then you can use JHymn:
http://www.hymn-project.org
If you have the latest version of iTunes, then I'm afraid there's no way as yet to convert them. This is why I tell people on here not to buy from the iTunes Music Store, or most of the other digital music sellers. So, don't buy anything more from iTunes.
For very cheap legal (with a loophole) downloads, in pretty much any format you like, try this:
http://www.allofmp3.com
I'd recommend downloading the FLACs if you want the highest audio possible (just the same as the CD the music came from), which you can then convert easily to mp3 or similar, and archive the FLAC files.