I am developing a Q & A Site for my students. I find stackoverflow an amazing example and would like to have something similar(if not this feature rich) for my course.

I am a sytem programmer not much familiar with web-application development. How do I begin. Database scheme, features, AJAXness etc. Can I get some existing codebase I can build on top of? Something opensource?

Language of choice is PHP. Any pointers are welcome.

Thank you in advance.

Edited: Added info


It shouldn't be hard to replicate using PHP/MySQL. It's not a very complicated site. plan out how you want all of the tables/classes to be laid out (Questions, Answers, Users, Tags,Rep,Badges,etc.) and start coding.

Is there any particular part that you are confused about or looking for advice about?

+2  A: 

It would be reasonably trivial to create something similar as a learning exercise, but the real value behind the stackoverflow site is the polish, attention to detail and vision that's gone into the site and associated branding/marketing, etc.

Irrespective, you'll probably find that you get more answers if you do the ground work yourself and then post questions for any specific architecture/design/implementation issues you get stuck on.

Also the critical mass of users add to the value of the site.
@Chris Yep. When the founder has a heavily trafficked software blog already, it helps...