Nope, it won't. This card is weak.
Beside, if you are using Radeon 9550, you probably have AGP interface, so you need AGP card (a bit old one these days) or new motherboard and PCI-E card. New motherboard will probably need new memory, processor (different socket), power supply and basically it will be new computer 
There are still some cards on AGP interface, but imo it's just wasting of money. You would have to buy something like Geforce 6xxx series or HD 4650 (the card you asked about, but AGP version). Well, I have 6600GT installed on my 2nd computer and imo it's just not enought to play even after set minimum level of details (game has ~15 frames per second, and to play comfortable you need double that value).
If you want gather some informations about graphic cards, I suggest you to check this website