problem using nested iframe

hello
i've got a document with iframe where i have a few input and textarea fields. then in this iframe i have another one which contains html document with form. after clicking save button (it's placed in teh first iframe), values from the first iframe's fields have to be written to the form in second iframe and the form must be submitted. I use this way simply to avoid reloading content of main iframe.

and my problem is: how to write this values? i dont't want to use document.all (i'm trying to use getElementById instead, but it doesn't work), I mean how to get the access to the second iframe's form fields. i was using many combinations of getElementById but i got an error that it's not an object or it's empty

thanks for help