NPD continues to report on holiday sales data; this time the research firm tells Next Generation that the Xbox 360 HD-DVD drive has sold 92,000 units since launch. The numbers break down into 42,000 in November and 50,000 in December, or roughly 2 percent of the Xbox 360 install base. With Microsoft claiming that the HD-DVD drive is selling out at retail, this would suggest either that Microsoft is having a hard time producing units or that they are limiting drive production for some other reason. While the HD-DVD drive competes with Sony’s Blu-Ray format, the Xbox 360 add-on might also be seeing competition from the Xbox Live Video Marketplace. Even though users can only rent HD movies via the service, owners of the Xbox 360 premium system don’t have to pay out for additional hardware. Every PS3 comes with a Blu-Ray drive, so total sales for that format look good, but one will have to look at movie sales rates to get a true indication of the relative popularity of the competing formats.