On a 2002 MG ZR 120, the immobiliser prevents the engine from starting without the correct key or fob. When the key is turned in the ignition, a transponder in the key communicates with the car's immobiliser system to confirm it's authorized. If the system does not recognize the key, it disables the fuel supply or ignition, immobilizing the vehicle to deter theft. To reset or disable the immobiliser, you typically need to use the correct key or consult the vehicle's manual for specific reset procedures.
That would depend which MG it is. Modern (approx. post 2000) MGs are based upon Rovers but given different names and turned sportier. For example the Rover 25 was converted into the MGZR which has then been used in races and is more appealing to younger people
To install a new window regulator on a MGRZ driver's door, remove the door panel and the wiring attached to the power window mechanism. Remove stereo speaker from the inside door and the window glass. Remove the old window regulator and replace with new.