is it possible to build a website and have it so people can sign up so they can earn points (sort of like kiwibox or neopets) or do you have to be some big company with lots of money to pull off a project like that?

I guess its possible..youd just have to assign the points manually i suppose...which would end up being quite timeconsuming, I'd imagine...

Yes its possible you can do it with php like when someone votes on a poll they get 4 points. or when they make a post, their number of posts increases :) you'd need a database tho or you do do it with cookies and javascript