The Zune all you can download for $15 has really caught my eye.?

I'm basically mp3 illiterate. Both of my sons have sansa mp3 and I rip music from cds for them to their mp3, and my mom has an ipod and she just rips from cds as well. Question is, if I get a Zune and do the monthly fee, will the songs that I download to my Zune also be able to be downloaded to my kids mp3s and my mom's ipod?? Does it create a file that is not compatible with only the Zune??