Outlook 2003 users can change how long the Desktop Alert is displayed. This is the blue rectangle which displays on the screen when new mail arrives and is also known as "toast". (It's not to be confused with the New mail alert window which is controlled by Rules and supported in all versions.)

The easiest way to configure it is using the Tools, Options menu, Email Options, Advanced, Desktop Alerts Setting button. You can adjust the time it remains on the screen and how transparent it is. (Adjust the screen location by dragging the alert to another position.)

The maximum time is 30 seconds, if you need longer, you can edit the registry.

Browse to HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Common\DesktopAlerts. Add a TimeOn DWORD key (if not already present) and set a value in milliseconds, up to 4 billion worth (50 days.)

This registry key also holds the values for the screen location and transparency. (These keys are created when you change the default settings.)