It will cost you 400 Microsoft Points to import tracks from Dance Central into Dance Central 2, Microsoft has revealed on Xbox.com. Alternatively, anyone who pre-orders the sequel will be able to import the tracks for free.
In order for the process to work (irrelevant of whether you've pre-ordered or not), you'll need to submit a code found on the manual for Dance Central - if it's already been redeemed (perhaps if you bought the game second hand) you're out of luck.
All DLC tracks bought for Dance Central will automatically be imported into the sequel. Dance Central 2 hits stores for Kinect for Xbox 360 on October 21.