I borrowed my friends mercedes s 500. The car starts but even with my foot on the brake wont let me shift into any gear. Any ideas

There is a lever between the front seats with a somewhat phallic knob atop it.

Generally the road drive positions are indicated in S.A.E.format.
Try moving it to the letter D.
If a Standard 4 or 5 speed tranny with a clutch,first depress the clutch pedal{the one foot pedal far left next to the brake,upon which pressure will impede the forward progress of said vehicle}and then attempt to engage said gears by shifting into any of the indicated patterns.

Kindly let us know what format{I.E.standard or automatic}this vehicle is equipped with,all the best

this car has an automatic transmission, its starts but will not shift in to any gear. when I remove the key and open the door a message on the dash reads remove chip with a picture of a key and says dont forget

Well you may want to go to the tech forum here,may be a neutral safety switch issue or a more complex thing.

What year is it? generally a code reader will indicate problem areas on '91 and more prominently '96 and above.

Just tell me what else you notice when you press your foot on the brake firmly and place the shift in 1 2 3 or D?

it is a 2001 I apply the brake but the shifter (automatic) wont budge