Dual monitor game problems

Ive just recently got a new computer and two new screens but when i play (for example Counter-strike 1.6) ,my second monitor goes black and i cant use it. i cant figure out what is the problem or if there a option that i missed because every thing works great and i can use my two monitors but when i play a game full screen it goes on my first monitor ok but my second goes black and i cant use it.I have vista so i dont know if thats a problem or maybe my video card?

Here is my spec:
Video Card:Saphire HD4870
CPU:Quadcore q6600 2.4
Motherboad:Asus p5q -e
screens:samsumg 20" 5 ms (two of them)

Thx alot for your help,its really appreciated.

I dont think that ATI supports stretching the screen to two monitors.
I have two samsung 24" at 3840*1200 and my old (hah) 4870x2 would not support it. The second screen goes blank.

BUT I think my problem was because I had a CrossFireX setup...meaning the 4870x2 card is two 4870's in one and that does not support the 'stretching'...your 4870 might support it...check with the CCC software.

ya its okay if counter strike only plays on one monitor but the thing is that i cant use the second for anything when im playing ,it turns black and i dont see my desktop.Mouse my can go on it but as soon as i click on the monitor it alt-tabs my game.

Thx alot for the help.