function changeArea( to ){
    toarea = document.getElementById( to );
    activarea = document.getElementById( activ );
    
    if( toarea && activarea ){
        activarea.style.display = 'none';
        toarea.style.display = 'block';
        
        // CHANGE NAVI
        
        if( to == 'prf_home' ){
            document.getElementById( 'lnk_home' ).className = 'active';
            document.getElementById( 'lnk_gallery' ).className = 'unactive';
            document.getElementById( 'lnk_guestbook' ).className = 'end';
        }else if( to == 'prf_gallery' ){
            document.getElementById( 'lnk_home' ).className = 'before_active';
            document.getElementById( 'lnk_gallery' ).className = 'active';
            document.getElementById( 'lnk_guestbook' ).className = 'end';
        }else if( to == 'prf_guestbook' ){
            document.getElementById( 'lnk_home' ).className = 'unactive';
            document.getElementById( 'lnk_gallery' ).className = 'before_active';
            document.getElementById( 'lnk_guestbook' ).className = 'end_active';
        }

        activ = to;
        return false;
    }else{
        return true;
    }
}