DHTML background opacity

Hello :

I am using DHTML filter : opacity to fade background image. But the difficulty I am facing is that the entire page fades, inted of just the background. I don't have much experience in DHTML.

I am including the stylesheet code which I am currently using :
body.main
{
filter:alpha(Opacity=15);
background-attachment: fixed;
background-image=url("GSG_logo.gif");
background-repeat: repeat-x,repeat-y;
scrollbar-base-color: white;
scrollbar-dark-shadow-color: white;
scrollbar-face-color: blue;
scrollbar-highlight-color: white;
scrollbar-shadow-color: black;
scrollbar-3d-light-color: white;
}

I am sure something's wrong with the code, but not sure what part, and how to fix it.

Can anyone help me solve this code problem ?

Thanks,
RAD