<div style:position: absolute; left:50px; overflow: auto; top:200px; right:100px; bottom:25px;>
Method 1 and then consider to store a cookie with the scrollbar position.
Method 2 or store the value server side in a visitors table on base of the IP
There is one more funny way.
use anchors like
<a name="foo"> and send your post action to the URL containing the anchor like this
<form action="site.php#foo" ... Its not so exact like the cookie version but it works somehow :))