I've used the below before, and it has worked. It isn't very pretty, but you can alter it to suit your needs.
The following JavaScript function grabs the location.href & document.title for the sharer, and you can ultimately change these.
function fbs_click() {
u=location.href;
t=document.title;
window.open('http://www.facebook.com/sharer.php?u='+encodeURIComponent(u)+'&t='+encodeURIComponent(t),
'sharer',
'toolbar=0,status=0,width=626,height=436');
return false;
}
Usage:
Share on Facebook
It looks like this is what you could possibly be looking for: Facebook sharer title / desc....