Form Validating

Dear Friends,
I've a form with some fields to be cheked.

I've a page to check the fields and then if all are ok then update or write a file.

My problem is that when a field is wrong I would like to display the form page with a message near the field wrong and the value into the rest without retype all the value.

I can do all the thing except to have the fields filled. 

Please Help.

Thanks Michael,
but  How to do a postbak ?

Bye

What I'm using now is exactly response.redirect whith the error code.
I can pass back the error type like 1 is wrong name 2 Insert code 3 .... Etc. But if I wont to allow the user to don't retype all the infoemation I dont wont to have a response.redirect 1Km long.

Do you know another way ?

Bye.