Captain Rebecca, I can't help with a tablet or laptop pc but I can tell you that a GF FX5600Ultra 256mb card will work fine and show all the eye-candy the newest graphics cards will for SHIII. I've run this one for a year and a half and find it works just fine.
And on another note for a bit of advice...... I'd wait until Windows Vista comes out and then look into a new tablet/laptop or desktop pc. Vista will be the deciding factor for gaming seeing it will use DirectX 10. And if you want a new desktop, build one or get someone to help you build one. It's the only way to go if you want to upgrade down the road.
