Stay away from CS. Unless you have been playing FPS for a while now, CS is going to be too hard for you. You ain't gonna have fun if you're getting fragged every second. Pick an easier FPS game to get into to.
I tried CS back in 2005 for the first time and couldn't last 10 seconds without dying.
well ive had css since launch back in 2004. i think its great and i still have it installed, its definatly one of those games you will buy and keep on playing. granted i dont play it everyday but every once in a while i feel the urge to play it.
to start off with i would keep to small deathmatch servers until you get used to the game, maps and aiming.
as for trying before you buy, ill see if i have a guest pass or something.
EDIT: sorry i dont have a guest pass for it, but isnt it just like £5 off steam?
oh and your card will handle it fine, granted your cpu is up to the task. (id say at least a low end dualcore for comfortable gaming).