just read the question by chidave, and i have similar trouble with some games although mine sound a bit different, as follows, one game in particular, call of duty, runs ok when the action is in a room or a building, but as soon as it gets outside everything slows down, it normally seems to happen more with more complicated games like medal of honour some simulator games, but others like splinter cell work fine . any ideas please. D
holmesy67, as per woodchips post, it depends on how serious you are about gaming and what games you would like to play in the future.
The slow down you get when you're outside is indicative that your card is struggling. Your games would play a lot smoother with a more powerful card.
As you currently have an ATI card it would be easier if you stayed with this brand because if you changed to a card with an Nvidia chipset sometimes you end up having to reinstall you operating system to cure driver conflicts.
As to what card you get, then it's just a question of how much you can afford/are willing to spend.
If you need advice as to what card to get, just post back with an amount you willing to spend, what operating system you're running on, how much RAM you have and and what processor is in your system and someone will point you in the right direction.