or_timelords: ([10] brilliant!)
The Doctor leads Jack to his TARDIS and unlocks the door. This bit is always exciting, "testing out" a new companion, seeing if they can get along. How they react to the peculiarities of the TARDIS is usually an important indicator; however in this case, Jack's already met other Doctors. He probably knows what the inside of the TARDIS looks like.

"Mi casa, tu casa and all that," the Doctor says as he pulls open the TARDIS doors and gestures for Jack to step inside. As Jack passes him by, the Doctor has a very brief moment of doubt--this man's a soldier, he's military, or ex-military, and with the exception of the Brig, the Doctor isn't fond of military men. But then he dismisses these thoughts. He's always tried to keep an open mind, and Jack seemed likable enough when they'd talked just a moment ago. If they don't get along, the Doctor can always bring him back here to the multiverse.

"Now then." The Doctor pulls the door closed behind him and jogs up to the console, smiling at Jack. "Where would you like to go? Eridani 4, vast deserts and red mountains and a sister planet in such close orbit that it fills the whole sky at night? Nulelabaj, a planet covered in a thick forest of living, talking trees? Or maybe Aiqy, the 64th century party planet? Or-- do you like surprises, Jack? I can set the TARDIS on random. She goes anywhere in all of time and space, and if I put her on random, we could come out anywhere."