The OS is the operating system of the mk4 nav computer and controls all the nav function and well as the GUI (screen interface).

Download one of these.

v32 OEM (with ===BMW=== splash screen).
MEGAUPLOAD - The leading online storage and file delivery service

v32 Nightmode (with landrover oval)
http://www.megaupload.com/?d=MA8WG2XA

Once you have downloaded the file, unzip it (using winzip or similar) into a sub-dir on your pc.

Then use imgburn or similar (The Official ImgBurn Website) to burn a new (blank) cd with the new downloaded firmware image.

v32 is the latest, but has no updates for the mk4 over v31).

unzip imgburn, then v31 image and then open imgburn, and select the "write image file to disc" then select the v32.cue (i think) file.

Select the write speed as x1 (or the slowest rated speed for the disc, you must do this) and then burn on a good quality cd.

When its finished writing your new firmware cd,
Go to the car open the drivers door,
Go to the nav computer and press eject on drive,
Eject the map disc,
Switch ign to pos 1, leave door open.
Insert firmware disc into drive, follow instruction on nav screen.
Wait (approx 6 mins) till sat nav asks to eject cd and reboot.
Eject cd, and remove from drive
Confirm reboot.

That's it.

Do not switch off ignition or close the door when doing the upgrade.

__________________
Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.