It is not possible to change the video card. It's not a normal card, it's built into the motherboard, I think.
It IS expected that Apple will update the mini soon, actually, but I have no idea what that means. It could just mean more RAM and larger hard drives for the same price. Or it could mean something else. There's no way to know.
Thanks again Jeff. I saw the imminent annoucement at thinksecret, and was hoping they'd upgrade the memory card to at least a 9600. For those of us who don't care about performance and only about getting up to speed on FCP & Motion, it would be nice to have the option of a cheap machine.