|There are lots of Hp pavilions, which model do you have? (e.g. dv6, dv7, e.t.c.)|
Look at the bottom of the laptop to see the model #.
From what I know is that Windows Vista/7 display drivers by default keep the aspect ratio instead of stretching to full screen when running full screen 3D applications.
What you need to do is go to the display driver's control panel, and under 3D settings select an option for stretching to full screen.
You could set the game to run at the maximum resolution your monitor can offer (native resolution), e.g. 1280 x 800, 1360 x 768, 1440 x 900, 1680 x 1050, 1920 x 1080, 1920 x 1200 e.t.c.
E8500 | 3GB | 320GB | 9800 GT 1GB @ 720/990 | HP w1907 @ 1440 x 900 60hz| Win7 Ultimate x64