Those are similar specs to my laptop, which only runs it smoothly at 800x600 resolution, with everything on medium-low graphics.
Well... It really depends mostly on the quality of the graphic card which I think will be fine. The physics on the other hand is calculated with CPU, mostly.
If Penguin_lolwut didnt buy the game yet, I suggest to try it first. Then you can see if it's possible to play it with decent Anti-Aliasing and resolution, something higher than 800x600. T_T The Strip would be a good place to test your graphics. If you have any idea where that is, of course.
Because as Red said, more stuff there is, whether you see it or not, will decrease performances. Quest scripts that has very little delay, Cubic activators, objects, npcs and special effects will all be processed at the same time or kept into memory. Some of those, like quest scripts and certain NPCs will keep processing even when you are out of that cell. Obsidian did a great job at that, they did everything they could to ensure a smooth gameplay, even modifying quest script delay within the script itself, to make sure you've got the highest FPS possible even for a few milliseconds. The Cell system also helps a ton, kinda like a Field Of View. (which they also have)
One good trick to test your RAM and computer is to boost your speed multiplier above 5k then run in a straight line. That will effectively load one cell after the other, at an incredible rate until the game crash because your computer can't handle that much. If you don't crash then you've got a better comp than mine or running it smoother than I am.