From what I've heard, Spore won't be that graphical intensive, and again, from what I've heard Will Wright have stated that the game will be about the same as The Sims 2. But if I should guess myself, I would say that the game look like it's going to use some CPU power
hehe.
Here's also a link from sporeWiki about the system requirements:
http://www.sporewiki.com/System_requirements
A very nice site
If you look at the estimated graphic card that can be used, it can't be Vista only. But we'll see how it goes when EA is going to officially show us the system requirements.
Also, here's a collection of short video clips showing off some different stages for a creature. It's very nice:
http://www.sporewiki.com/Spore_Videos_from_GDC_2007
I wonder what kind of crazy content from Spore we're going to see from players when it has been released for some time.