Some of the top technology companies, including Intel, Microsoft, Dell, and Advanced Micro Devices joined forces Tuesday to form the PC Gaming Alliance, which will try to promote the PC as a gaming platform.  The alliance will bring hardware makers, software companies, and game publishers under one roof to "accelerate innovation, improve the gaming experience for consumers and serve as a collective source of market information and expertise on PC gaming," the alliance said in a statement.  The alliance comes at a time when PC video game sales are falling. PC games sales in the U.S. were $910.7 million in 2007, down from $970 million in 2006, according to research from NPD Techworld.  Unit shipments of PC game software totaled 36.4 million in 2007, compared to video game software unit shipments of 153.9 million, according to NPD.