[alf]

Do it. 1 week in Beijing is enough to see all the sights at a leisurely pace. Take the last day before you leave to just chill out before the flight. You could even take a overnight trip to Xian to see the Terracottas if you want to jam it in.

Allow a day for the Wall, go to the more remote section (mutianyu i think), charter a car.
A day for the Forbidden city and surroundings, catch a cab or subway.
A day for Summer Palace and surroundings, cab or subway.
Check out the Hutongs. Walk around, get lost and find yourselves.
Half a day for Temple of Heaven, there is a tourist trap shopping center right by there for the other half a day. Cab or subway.

Beijing traffic is terrible and the city is massive, subways work nicely to move around the city. Cabs do ok for shorter trips.