[mod_python] mod_python advice needed

> 1. create a login page (session, cookies, auth) manage the state of the 
> user (i want to track this in the backend)

That is web programming "in general". If you have a DB in place already, 
it makes sense to use that for your authentication and session 
management. Less session is better, usually an authorization cookie is 
enough and further session data is not needed.

> 2. create a page where users can place orders, I would like to be able 
> to do a post data without having to redraw the whole page.

That would require some Javascript wizardry. Though probably possible, I 
strongly advise to consider whether this is really a "problem". It's 
like building a plane and requiring it to float - it will never be a 
good boat that way.

Click a button/link and go another page is the way it's supposed to be.
I have done continuously (every 1 sec) updating graphics for a home 
security system, and when built smartly (simply using caching, without 
any client side scripting) it updated sensor states without even a 
'flicker'.