There's a new capability in views in Outlook 2003 such that each message can take up two lines in the view, instead of one. Some people find that with the reading pane enabled on the right-hand side, this makes it easier to handle mail without ever opening it.

You can configure Outlook to automatically go to a two-line view when it doesn't have enough screen real estate. This setting is configured here:

View | Arrange By | Current View | Customize Current View | Other Settings | Use multi-line layout in widths smaller than [ X ] characters

By setting it to "80", that means that whenever the Outlook pane with the list of messages shrinks to fewer than 80 characters wide, it will automatically use a two-line view.