• 1 GHz processor (32- or 64-bit)
• 1 GB of RAM (32-bit); 2 GB of RAM (64-bit)
• 16 GB of available disk space (32-bit); 20 GB of available disk space (64-bit)
• DirectX 9 graphics device with WDDM 1.0 or higher driver
They're a little bit different from the minimum specs put out for the January beta, in that it slightly pumps up the requirements for the 64-bit version of the OS (but you want at least 4GB of RAM to really take advantage of 64-bit anyway). You'll notice they're practically the same as the requirements for Vista, but unlike Vista don't vary from version to version—these are the specs for every version of Windows 7. You can see how each OS fares on the same hardware right here, for something more concrete.
And, while these specs might have seemed steep when Vista arrived, if your computer doesn't meet them at this point, it's time to buy a new one (with Windows 7 installed, natch). [ZDNet]