I would go like this:
1. Make a website that just replies "Hello World"
2. Make a website that just serves static pages
3. Make a website that is just a single form and when you submit it, it just echos the raw stuff back
4. Make a website that actually does something with the stuff from the form
5. Make a website that is a guestbook
6. Make a website that is multiple guestbooks
7. Make a website that is multiple guestbooks and anyone can add new guestbooks
Then you just rename guestbooks to threads and you have a textboard.