If you'll be doing ANY gaming, EVER, you'll notice a huge improvement. It might make a difference for DVDs/DivX-type video also, just in terms of not lagging, but I'm not sure on that.
Also take the person's advice about getting RAM separately. RAM is important, but Dell charges like 400 % of the actual cost.
EDIT: Whoops, I be late, you followed both advices, LOL. That's what I get for not reading.