I don't know if I got it right, but does this solve your problem?
I just changed the overflow-y: scroll;
#content{
border: red solid 1px;
overflow-y: scroll;
height: 100px;
}
Edited
Then try to use percentage values like this: http://jsfiddle.net/6WAnd/19/
CSS markup:
#body {
position: absolute;
top; 150px;
left: 150px;
height: 98%;
width: 500px;
border: black dashed 2px;
}
#head {
border: green solid 1px;
height: 15%;
}
#content{
border: red solid 1px;
overflow-y: scroll;
height: 70%;
}
#foot {
border: blue solid 1px;
height: 15%;
}