Auto-Refreshing without loosing focus (scrolling)

I have an autorefresh on my site because the content changes every few minutes. The problem is, when someone is reading that site, and is scrolling down, the autorefresh will bring him always back to the begining of the page and he has to scroll back to continue reading. As you can imagine this can be really annoying. Now, i have seen on some Web-Chats, they somehow refresh the chatwindow and you dont even see the refreshing process. The new posting are always added at the end of the site and if i scroll back to read some older postings, the new postings that are coming in doesnt make the browser scroll back to those new postings. I have no clue how they do that. So, it would be really great, if someone could help me on this. Thanx!