Varied connection speed per computer with router

Ok this is driving me crazy, I have above average computer knowledge but lack in networking knowledge. The issue is my belkin n router supports speeds up to 300mbps, my wife’s computer connects at that speed. She is running Win7. My computer (vista), which has a intel 5100 wireless card that supports that speed, will only connect at 150mbps.

No matter what settings I adjust, that is the best I can do. No matter where I am in relation to the router, the speed will not change (of course if I get far away it drops). Even when it is side by side with my wife’ she still gets 300 and I get 150.
What am I missing? What setting have I got wrong? I have current and best firmware for the router and most current driver for my wifi card.

I feel like I have something simple set wrong.

Thanks