Ask Engadget: Best setup for DJ'ing with a PowerBook?

It's Thursday, which means it's time for another round of Ask Engadget. Last week reader Colin E. wanted some recommendations for a good digital media adapter, this week Boris B. wants to know,

I was wondering what suggestions people had on what kind of setup would be good to be a DJ with only a PowerBook
and maybe some digital turntables?

Anyone out there have any suggestions for how Boris can best get busy on the virtual wheels of steel?