Well, since Shugo Chara OSTs aren't distributed or licensed in the US, downloading wouldn't be a legal problem since Japan's laws can't be enforced on people in the US. At it's core it would be illegal because you're taking something that's not yours but at the same time, it's impossible to punish you *if* you're even caught to begin with. (And Japan tracks down people who uploaded the content and punishes them rather than the people that downloaded it. You see it for manga all the time in the news.)
You can download the torrent for free here:
http://www.bakabt.com/143506-shugo-chara-music-collection-nipponsei.html