Apple has many restrictions on music downloaded from iTombs, I mean, iTunes.
You can't easily move songs to another computer, and I would guess that if you do uninstall iTunes, you may not be able to access the music again.
The iTunes audio format is .aac and you can't change any settings to make them download as mp3.
There are some programs out there than can unlock the iTunes audio files so you can move them around. Take a look at
www.sourceforge.net and do a search on that website for iTunes unlocker, or iTunes converter. I've seen some programs there that can help free your music.