var div = 4;
var sliderEnabled = true;
function scrFol()
{
var ad = document.getElementById( 'slider' );
var dPos = ( document.all ) ? document.body.scrollTop : window.pageYOffset;

if ( ( dPos == 0 ) && ( document.all ) )
dPos = document.documentElement.scrollTop;

dPos += 50;
var cPos = parseInt( ad.style.top );
if ( cPos == 0 )
cPos = dPos-1000;

var posDif = dPos-cPos;

if ( ( ad.style.display == 'none' ) && ( sliderEnabled ) )
ad.style.display = 'block';

if ( posDif > 0 )
ad.style.top = (cPos+Math.ceil(posDif/div))+'px';
else if ( posDif < 0 )
ad.style.top = (cPos+Math.floor(posDif/div))+'px';

if ( sliderEnabled )
setTimeout( 'scrFol()', 20 );
}
function closeFollowSlider()
{
sliderEnabled = false;
document.getElementById( 'slider' ).style.display = 'none';
}

setTimeout( 'scrFol()', 2000 );