$150 could, I'm sure, get you a 9800 in Yankl'nd. They're rather superior to the 9550s. They're alright cards; I have one at the moment.
You might be wasting your money, though. What's the rest of the PC like? Use FreshDiagnose (freeware) to find out if you're unsure.
Don't buy anything if you're not sure of what you're doing. A lot of people here will be able to advise you as to what will work if you ask us and give us sufficent information.