Many of my users are reporting that after the application of the update listed in KB918899 the browser crashes in SharePoint when the user chooses “Design this Page”. Uninstalling the service pack and reboot to resolve the issue. (Or put the page into design mode by selecting “Add Web Parts“ instead of “Design this Page“.)
It appears from this notice MS06-042: Cumulative security update for Internet Explorer that Microsoft is aware of some of the issues. The word is that a fix for this issue will be part of the October cumulative update.
Here is the news thread that got us going in the right direction.