Screen Resolution !!!

i am learing web designing. i made a web site when my screen resolution is set at 600*800 pixcel, but when the screen resolution is changed, my web page layout is going to out of focus and scroll bar appears.
well is there any script or tip that what ever is the screen resolution of the user is set my web page automatically adjust with it. so the user can see all the page stuff correctly.
thanx 4 ur help !!!!