Since version 5.2 of the drivers, this feature was removed because Windows 7 has all of the functionaility as a part of the WIndows Display Properties.
To quote the release notes:
On Windows 7, the configuration of a DisplayLink device is now achieved through the use of Windows Display Properties (WDP). The WDP provides the user with a simple method to attach, rotate or duplicate screens as well as modify screen resolution. WDP is accessed by right-clicking on the desktop and choosing "Screen Resolution". It can also be accessed through Device Folder (Devices and printers on the start menu), right click the DisplayLink device and choose "Display Settings". The DL-GUI is no longer used for display configuration, and no longer has such menu items.