This can be achieved from within the system registry by modifying the Outlook settings to place the minimized Outlook icon in the system tray. You can then maximize the program whenever you want by double clicking the icon.
Here is how it can be done:
1. Click Start, click Run… and type regedit or regedt32 and then click OK. This opens your System Registry Editor Window.
2. From the left pane of the Registry Editor window, navigate to the following registry key
3. Now, in the right pane create a New > DWORD Value and set its Value name as MinToTray
4. Edit the MinToTray DWORD Value just created by double clicking on it (or) right-click to choose modify and change the Value data to 1 in Hexadecimal mode and click OK. Finally Close the Registry Editor.
That’s it!! From now-on-wards whenever you minimize your Microsoft Office Outlook 2007 it will be minimized to an icon into your system tray and if want to disable this setting or re-enable it again, you can do it all from your system tray itself.
All you have to do is, right click on the minimized outlook system tray icon and select/deselect Hide When Minimized option from the menu.