If you are running OWA and you just installed IE7, you may need to ensure that you have this hotfix installed on your server
In the upcoming Microsoft Windows Vista Beta 2 release, the Dynamic HTML Editing ActiveX control is being removed from the Internet Explorer browser. As a result, there is functionality missing that Microsoft Exchange Outlook Web Access relies on. This update replaces that deprecated functionality on the Microsoft Exchange servers so that Microsoft Exchange Outlook Web Access continues to function smoothly.
Now if you are on Exchange 2003 sp2, you probably already have this installed…..as it comes down via Microsoft Update.
A more specific patch can be found here but I'm finding that with merely that prior Vista/eola patch on the box my OWA is working just fine…but review this one as well:
Rui blogs about the update patch here: but the older one works as well.
The Compose Message form stops responding after you install Internet Explorer 7.0 and the S/MIME control on an Outlook Web Access client in Exchange Server 2003: