Tabbing to control in an IFrame

Here is my setup....
I have an ASP.net page with three areas on it. One of these areas will have a lookup dropdown list. When the user chooses from this dropdown list, the rest of this area will pre populated based on a hit to the database. My issue is, to only have that part of the asp.net page refresh. I was thinking about using IFrame's for each area. BUT since this is all on one page, how do I set the tabbing from one control on one IFrame to another control on a seperate IFRame? OR is there a better way of doing this without using IFrames?

Thanks for any help

First, what is wrong if page gets refereshed, it does not look too "heavy" anyway.
Second, I would try to play with PlaceHolder control instead of IFrame