Microsoft Windows Vista Ultimate UPGRADE Limited Numbered Signature Edition DVDs are available to purchase on Amazon:
http://www.amazon.com/Microsoft-Windows-Ultimate-Numbered-Signature/dp/B000M2WPIQ/ref=pd_sim_sw_2/104-1611751-7630347
It looks like there are going to be 20000 such DVDs, signed by Bill Gates.
Product description from Amazon:
The most comprehensive edition of Windows Vista, Vista Ultimate Upgrade Signature Edition (DVD-ROM) is the first operating system that combines all of the advanced infrastructure features of a business-focused operating system, all of the management and efficiency features of a mobility-focused operating system, and all of the digital entertainment features of a consumer-focused operating system. For the person who wants one operating system that is great for working from home, working on the road, and for entertainment, Vista Ultimate is a no-compromise operating system that lets you have it all.
Sounds pretty good to me. And it's signed by Bill Gates. Did I mention that already??