The graphics core in AMD's Llano APUs comes in two flavors; HD 6550D (A8 series only) and HD 6530D. The HD 6550D is about the equivalent to the desktop Radeon HD 5570, the HD 6530D is about equivalent to the desktop Radeon HD 5550.
As a comparison, the Intel HD 3000 graphics core found the "k" models of the Intel's 2nd generation of Core i5/i7 (Sandy Bridge) is a little more powerful than the desktop Radeon HD 5450. This is around 2x faster than their older GMA 4500MHD graphic core. Non "k" Sandy Bridge CPUs (i3/i5/i7) will have the slower Intel HD 2000 graphics core.
I believe the Xbox's ATI Xenos video card is approximately almost as powerful as a Radeon X1900. Granted, the Radeon 5570 video card is based on an architecture that is 4 generations newer than the Xenos (Radeon X1900), but I think Xenos is still more powerful.