-----------------------
|.........|................. |
|.........|................. |
|.div 1_1.|.....div 1_2..... | <- Div1
|.........|................. |
-------- ................. |
|........................... |
|........................... |
|........................... | <- Div2
|........................... |
|........................... |
----------------------
<div1>
<div1_1 width="30%"> ... </div>
<div1_1 width="70%"> ... </div>
</div>
</br> --line break
<div2> ... </div>
place your each group of controls inside individual update panel to avoid whole page's postback.
Happy Coding!
:)