The whooping tunnel goes from by the Cutty Sark The Emirates cable car goes from by the Dome they are several miles apart
Option 1 Park in car park 2 at the Dome (for the tube station, £11 a day) then get the cable car and spend some time in THe Crystal - by the north terminal if its a nice day, yomp up to the Olympic park or just mill about the docks and then get the cablecar back and then explore the Dome - there is loads to see and do in and around it you'll spend most of a day
Option 2 Park in Greenwich - personally I'd park at the Maze Hill bottom corner of the park Walk to the Cutty Sark, see Gypsy Moth do the Whooping Tunnel the Maritime Museum walk up through the park to the Meridian, the Oservatory and enjoy the view from General Wolfe
we live in N london and do a lovely (for small boys) round: Overground and DLR to cable car (N side) then boat back up from south side - we go the whole way to Embankment and then bus/tube home, but you could easily do 1 stop and get off in Greenwich.
is not far to walk between them - half an hour? - but bleak and dreary. boat much more fun