Things u need:

1. Horizon
2. Your Memory Device (Hard disk or USB Memory)

Instructions:

1. Copy your profile to Your external hard disk or USB flash memory.
2. Open Horizon
3. Copy the Contents (Select all the files) from My folder to Horizon (Drag and Drop)
4. It will ask to which profile. Select your Profile and thats it. All the tracks will be copied
5. Go to the game. Track Central. And there u have in the sections. Enjoy

OR

Copy all files to [ur Device]:/Content/E00007B148BFEB17/58410AAD/00000001/(here)

Note: Works in Internal HD as well. You just need to copy ur profile to USB Flash, Open in Horizon, Drag and Drop the files, plug back in and move all back to hard disk.