This isn't a software problem. The fact is that the screen doesn't extend all the way to the edge of the panel. If you counted, pixel by pixel (like I have on my 15" MacBook pro), there are 1440x900 active pixels. On the newer MBPs, they have done a better job at filling the entire panel with active pixels. The border you're complaining about is built-in to the panel (and it's like that on most laptops you'd find).
According to your comment to Paul R's answer, what you're seeing is actually the space that the dock reserves for itself. It also helps emphasize the shadows of the windows. There's no way (to my knowledge) to change this (although myself and many other Mac users I've talked to much prefer this).
Apparently, this can be changed by moving the dock to the left or right side of the screen.