Ive been trying to sort this problem too...my recently acquired Passat estate, which I am not sure, B6 ? B7 Local dealer tells me its a 'C3' that's all I need to know !!!
Anyway...heres what my 'Owners Manual' says ... 'word for word'
Second speedometer display (mph or km/h)
In addition to the tachometer display, the speed can also be displayed in another unit of measurement (mph or km/h) while you are driving.
To do this, select the menu option 'Second speed' in the Settings menu.
Start the engine.
Press the button (shows a small pic of two rectangles joined in one corner...If you have this model, this is the small button to left of rev counter/temp display) press 3 times.
The odometer in the combi-instrument display flashes.
Press the button '0.0/Set' (If you have this model, this is the small button to right of speedometer/fuel gauge) Once.
The vehicle speed in "km/h" or "mph" is shown briefly in the display instead of the odometer.
This turns on the second speedometer display.
It can be deactivated in the same manner.
It is not possible to switch off the second speedometer display in those countries where the law stipulates that the display cannot be deactivated.
Hope that helps someone somewhere...it didn't for me ! I seem to be stuck with KPH !!!