For that, we rather look at Steam's hardware survey. According to their January figures, Windows 7 64-bit surpassed Vista 32-bit as the second most popular OS among users running the Steam client with a 19.50% share. Windows XP 32-bit remains on top by far with 42% use, while the 32-bit version of Windows 7 is fourth with 9%, a clear indication that the move to 64-bit will take place in this OS generation.
It's also interesting to observe CPU adoption trends, where 2-core processors are the most ubiquitous consisting of 56% of all computers connected to Steam. Quad-core CPU usage keeps growing and currently stands at 24% versus 19% back in September, while single core models have dropped in about the same proportion from September's 23% to last month's 18%. Intel processors are used in 69% of machines versus 30.9% for AMD. The green camp also loses in the GPU department where Nvidia dominates with 65% of all installed graphics cards. The well regarded GeForce 8800 remains as the most popular GPU despite its age (we reviewed it back in 2006). More details on these and other interesting stats are available here.