Getting field value from Child window (Dialog box) - Redbox?

Hi All

I have a page in which I have a text field followed by an ‘add’ button.
When I click on the add button it should open another page or dialogbox(
having its own template). When this dialogbox/page is active I should
not be able to type in the parent page[ I mean something like redbox or
thick box]. The page/dialogbox have a text field and a submit button .
and when I type something in the diologbox/page, the entered value
should display in the field in the parent page.

I tried redbox & think box but I am not able to get the value back into
the parent window.

Please help…

Thanks in advance.