Hi Steve,
I think that this is a great idea. You could look through this
forum for some ideas on building learning communities.
IMHO, your biggest challenge is to establish a social
context(s) for sharing (as has been done here on Moodle.org).
We are just completing a two year project where we have a STudent Network as part of our portal at
http://www.cabweb.net. We promised to make an active staff network (called HELP) and to offer collaboration spaces for teacher-led
activities but we included the Student Network as something for students to take up if they wish, and generally they haven't

You could look at this
thread where students gave some ideas of what they might like.
I am not surprised or unhappy about this as I have always thought that a realistic student network would take place somewhere separate and be run by students- and maybe be what my colleague described as an "anarchic" network.
If you are successful with this Steve, you will need some resources, and you may investigate the possibility of sponsorship from, say, social networking sites rather than official education funds.
Have you heard of the site set up some years ago called revise-it (now defunct) where student shared essays, etc.? It got caught up in the whole plagiarism thing (but the reality was a little more complex). Anyway, if you could get hold of the people who set that up (try googling for revise-it or reviseit - they were from Manchester Grammar School and now probably working in the city or running dot.coms!), they would probably have some valuable insights.