If you have installed your Exchange 2007 Mailbox Server on a Windows Server 2008 server you may find an issue where the redirection from /Exchange to /OWA doesn't work.
You will get an error when you login like "The user name or password that you entered is not valid. Try entering it again."
This is because by default the IIS7 install doesn't include the following Role Services by default;
You can either install them by Adding Role Services by going into Server Manager -> Web Server (IIS) -> Add Role Services or you can run the following at a DOS prompt;
Theme design by Cameron McFie