No real way to fix this one. If the shoutbox is heavily used then it runs into the same general PHP chat issues of just being a high resource script. IE has the additional problem of only allowing 2 connections to a domain, so if it's slow to respond then it can tie up a connection. If a second tab is open or another ajax function is going on at the same time, like previewing a post, then both connections are tied up and can cause the hangs.
The only real thing that could be done on this would be to switch the shoutbox back to an iframe type thing. Then you end up with the annoying refresh every 30 seconds even when there is no new content.
