>>1,5
Just a suggestion, but you might want to think of using Python. It's easy to pick up, faster than Ruby but slower than Perl, and pretty powerful -- good for a summer project.

Good luck and I'm interested to hear any updates along the way. I'm playing around with an imageboard-esque script myself but I've go a lot to learn when it comes to CGI...

>>6
I don't think live post preview is all that necessary for an anoymous imageboard, seems more of an old-style forum type thing.