George Ou at zdnet has posted a great write up regarding Windows Vista and graphics hardware. One of the most common questions I get about Windows Vista is "will foo graphics card work on Windows Vista?" or "Do I need to get a new graphics card for Windows Vista?".
George's write up puts this in good perspective. Here's how I think about this - when you buy a PC, you're buying a set of tools both hardware and software, with which you plan to accomplish a set of tasks or go through a set of scenarios. The hardware you buy is very variable - but the software is pretty constant - in Windows XP, most people choose one of four operating systems: Windows XP Home Edition, Windows XP Professional, Windows XP Media Center Edition, and Windows XP Tablet PC Edition. The amount of "variety" in the OS is a lot smaller - but it still needs to accomodate the broad variety of hardware that's out there.
So with Windows Vista - we invested in making sure that when you buy a new PC, we make the most of the hardware you bought to run the software on. If you decide that you care about other things more than graphics processing horsepower - maybe mobility, power consumption, or form factor are more important to you - then we make sure that you still can run the operating system well. When you buy a computer with a great graphics system (intergrated or otherwise), you'll get more features that take advantage of it.