WordPress MU

My website http://saktolang.com is for a people who wants to post something to sell of something they want to buy.

Is there a way to change the way they create a new post?

I want to have a standard form like..

title:
price:
description:

how can I add the price text box?

Sounds like a custom post type, which will roll out more fully featured in 3.0. I think there's some bare bones support for it in 2.9. But, I haven't used it.