Writing a successful crossover

So, I'm sort of working on my first crossover fic, and it's a doozy - Doctor Who with Atlantis. Now, here's the thing, Doctor Who exists in the SGA universe. Anyone have any tips for dealing with that? Right now, I'm working on a Rodney sort of freaking out all "No no no, this can't be happening. You're a TV show" etc etc. But what else? Or is that enough? And do I have the Doctor and everyone look the same as on the show we see? Cos that would be kinda weird. I think. But then, who do they look like? And Jack has to be there and he has to look like John Barrowman.

Please help before my brain explodes!! :-)

GIP

Hehe. I watched the David Tennant Top Gear the other night and it was just too funny. I had to icon it! :-)