A lot of laptop manufacturers sell their vista systems with 1 gig to keep costs lower. In reality its cheaper to buy it by itself than it i sto buy it from the manufacturer when you customize your laptop. Crucial makes good ram and its not very expenssive. With Acer laptops you should have a compartment on the bottom of the laptop to unscrew and get to one of the ram sticks and the other is located under the keyboard which requires some doing to get to (on the old models anyway, the new ones may both be in the under compartment) You will need to purchase 2 1gig sticks because what you have now is 2 512mb sticks.
Did that make sense?