function cycleImage( imgElementId, imgFilenames, imgIdx )
{
	if( ++imgIdx == imgFilenames.length )
		imgIdx = 0;

	var imgElement = document.getElementById( imgElementId );
	if( imgElement )
	    imgElement.src = imgFilenames[ imgIdx ];

	return imgIdx;
}

var sponsorImageFilenames = new Array (
	'images/city_logo.jpg',
	'images/hospital_logo.jpg',
	'images/camp_logo.jpg'
);

var sponsorImageIdx = 0;

setInterval( "sponsorImageIdx = cycleImage( 'SponsorImage', sponsorImageFilenames, sponsorImageIdx )", 3000 );