Free and now available, but it's a pain in the ass:
The 120GB HDD does come with a piece of equipment not included in the Xbox 360 Elite--a cable to transfer content from older 20GB 360 HDDs. This comes as no surprise, as Microsoft said the Elite would not come with the accessory when it announced the Elite back in March. The company's rationale was that the Elite is intended for consumers who hadn't purchased a 360 yet, so no transfer should be necessary.
Following weeks of grumbling on game blogs, Microsoft is offering data transfer cables for free to Xbox 360 Elite owners for a "limited" time. However, to obtain a cable, gamers must first jump through a few bureaucratic hoops. First, they must download, print, and fill out an authorization form with both consoles' serial numbers. Said form must then be sent via standard US mail to a redemption center in Indiana, which will then send out an Xbox 360 data migration kit gratis.