Concurrent editing

Dear all

I'm a lecturer at the Universidad Polit�cnica de Valencia (SPAIN) and I want my students to create their projects using an online collaborative word processor for their in-class & out-of-class assignments. The flat fact is that my choice is somewhere btw Writely and Zohowriter. I prefer Zohowirter but I'd like to know if my students can edit & work simultaneously on the same doc (during our lab sessions for instance). That's the most important thing for me, so far, (I'm not interested in wikis). I'd appreciate if you could be specific about this question.
On the other hand, I'd like to know more about copyright issues, I mean, the problem of web 2.0 is how copyright issues are dealt with: I'm pro-creative commons and the stuff, but what if some of my students aren't and don't feel secure about uploading their projects to a Web 2.0 site like this. How can I explain to them that Zohowriter is a safe place?

Thank you very much for your help and for your work.

Elena B. Ruiz