Battlefield 3 won’t support Windows XP or DirectX 9.
BF3 Blog noted that the new Frostbite 2.0 engine left both Windows XP and DirectX 9 out of the technical specs. DICE developer Johan Andersson then "Frostbite 2 is primarily developed for DX11. XP & DX9 is _not_ supported, 64-bit OS is recommended. Lots of time to upgrade if you havent!":
DICE hasn’t officially stated that Windows XP won’t be supported, and according to Wikipedia, 44% or so of all PCs out there still use Windows XP. However, BF3 Blog noted that a recent Steam survey showed that 25% of gamers on Steam still uses Windows XP, so that indicates that XP is no longer a viable platform.
Way back when, Links 386 forced PC gamers everywhere to upgrade processors. Battlefield 3 may be indication that the time of WinXP is coming to an end, so now many be the time for some gamers to finally upgrade to Windows 7.