making controls sizable on a sizable form

Hi,

I'm sure I'm having a blond moment here but can someone tell/remind me how to set some basic form properties please.

I have a simple windows form which basically falls into 2 sections.  the top part has a few labels & textboxes ( + 2 radio buttons and a combo - not much though say 10 controls all together) then there is a large multiline textbox and a close button at the bottom.  If the form size is increased I would like the new space to be filled by the large textbox.  This is the only control worth sizing.  The other controls shoul djust stay where they are and remain the same size.  I'm sure I've done this loads of times before using the docking property but I am having trouble.  If I use fill (along wioth some panels) it takesd the whole form and wont allow for the other controls.  Using other commands just make it expand vertically OR horizontally.  Can anyone tell me where I'm going wrong?

Thanks.