Currently 2D tasks aren't hardware accelerated very much on the PC, aside from the occasional Avivo video acceleration. Down the road, the new Windows Presentation Foundation could change that, as it allows for full hardware acceleration when 2D apps are drawing the screen. Hopefully, there will be an Adobe CS3 or CS4 that can use WPF to hardware accelerate Photoshop filters and Illustrator vector drawing, tasks that currently bog down the CPU like crazy if you have a large file. The WPF framework is supposed to be part of a future service pack of Win XP, so you'll still be able to benefit from WPF without upgrading to Vista (you just won't get the Aero Glass eye-candy in the UI).
It'll be until at least this time next year until we see anything like this from Adobe, so I wouldn't worry about it too much in you current build. If you plan to keep your computer more than a few years, I'd make sure that it has a PCIe x16 slot so that you can toss in a dedicated GPU down the road when we start seeing some WPF-compatible Adobe apps shipping.