User blog comment:Ralok/Magic Moment/@comment-217683-20100829042650/@comment-1221773-20100829044300

The Slim uses different HDDs, ones from older models aren't compatible. So yes, you would need to transfer it.

You don't need a kit though. I was able to use one of my USB drives (the one I used was 4 Gigs). I transferred my stuff onto the USB a portion at a time, then transferred it into the Slim. You will need to go onto the Xbox website to transfer your game licenses (for downloaded content) from your old console to the new one; that process took only a few minutes. In addition, some DLC will require that you re-download it before it can be used, but that also takes minutes (the DLC packs themselves are not re-downloaded, I think the process is just a verification of licenses).