Okay, so STEAM must detect what video driver you have and offer the lastest updates for that driver.
By the looks of things I have a Windows 7 Home Premium 64 bit.
My video card seems to be an ATI Radeon 5670 HD (with a Dxdiag version of 32 bit unicode...is that the 32 or 64 bit you're talking about?)
Steam auto-detects your hardware then downloads the most recent drivers for you. The AMD 11.11 drivers are probably out, but they're just a preview version or a release candidate version before the official, final drivers are released on their website. Honestly, I'd wait to download drivers until you either have an official release, or you can get a link for AMD's website that has the download.
Also, your OS is Windows 7 Home Premium ~64 bit~ so you have a 64 bit system. So if you go to AMD's website (AMD and ATI merged a while back, so they're the same thing now) and mouse over "Find a Driver" near the top right corner, you'd enter this:
Desktop Graphics
Radeon HD series
Radeon HD 5xxx PCIe
Windows 7 - 64 Bit