the game needs at least 1GB memory and a geforce 6800 or better (ps a 7300 is not better than a 6800 even though the number is higher)
need for speed pro street can be pretty hard on the videocard at times because to play the game properly, you need to maintain a good framerate
if your short on cast, then do this, if your pc only has 1 memory stick in it, buy a 1GB stick to upgrade to 1.5GB memory, then get a geforce 8600 for $100
with that card you can max out almost every game except ones like crysis