Hang on a second; this is for a school, not an engineering firm where time is money.
A 9600 Pro will work fine, provided that you are willing to use the right drivers. I've had success with ATI's version 6.14.10.6368 drivers, for Pro/E 2001 Student (essentially a really early datecode of 2001). ATI's Catalyst drivers (i.e. the newer ones, within the last three years or so) perform very poorly, however. That more-than-3-window problem is present in new ATI drivers, but not with the version that I mentioned; with it, you can have a dozen windows open, each containing a >50-part assembly, and not run into any trouble. Sketcher is similarly improved using this older driver.
By the way, the Radeons do support OpenGL, however ATI won't certify them for CAD work, because it's not in their interests to do so for a card targeted to average computer users. They'd rather have you pay a ton of money in order to take advantage of the more refined drivers for the professional versions (i.e. the low-end FireGLs).
As for PCI, well, that's not great, but once again, if you can find a card with good driver support, the bus bandwidth will not matter. I can't stress this enough. You're not rendering 75 frames per second of full-motion, high-resolution, high-colour video; you're (generally) spinning low-colour-depth, low-detail parts, for which 30 frames per second is adequate. (Consider, do you notice the choppiness in your 24-to-30 fps TV picture?)
It's ALL in the drivers, with any remotely modern 3-D video card based on an ATI or nVidia chipset. Spend your money on more RAM or a better single-core processor; that's where it's best used.
(I reiterate: much of the above doesn't apply to an engineering firm where a $4000 workstation is the norm, to keep productivity as high as possible. But it will do perfectly well, for a school environment.)