$( document ).ready( preloadImgMenu );

function preloadImgMenu(){
    
    var total = document.getElementsByTagName( 'img' ).length;
    
    for( i = 0; i < total; i ++ ){
        if( document.getElementsByTagName( 'img' )[i].className == 'imgMenu' ){
            var er = new RegExp( /(.*)(\/.*)(\..{3})$/ );
            var link = document.getElementsByTagName( 'img' )[i].src;
            var result = er.exec( link );
            link = result[1] + result[2] + '_over' + result[3];
            var loadImg = new Image();
            loadImg.src = link;
        }
    }
}

function menuOver( men ){
    var er = new RegExp( /(.*)(\/.*)(\..{3})$/ );
    var link = men.getElementsByTagName('img')[0].src;
    var result = er.exec( link );
    link = result[1] + result[2] + '_over' + result[3];
    men.getElementsByTagName('img')[0].src = link;
}

function menuOut( men, link ){
    var er = new RegExp( /(.*)(\/.*)(_over)(\..{3})$/ );
    var link = men.getElementsByTagName('img')[0].src;
    var result = er.exec( link );
    link = result[1] + result[2] + result[4];
    men.getElementsByTagName('img')[0].src = link;
}