you might need to clean up your scene. try using clean up on your objects and also the optimize scene command (under file i think).

also, what size textures are you using? you may need to lower the resolution. If that doesn't work, try going through your scene deleting objects one by one to see if the scene will render without them - it may just be one object that's messing you up.

as for graphics cards, an nvidia quadro is pretty reliable. check out autodesks site - they should have a list of recommended cards.