<script type="text/javascript">  
function ShareToVk() {  
tltl = document.title  
width = 550  
height = 268  
w_top = (window.screen.height - height)/2  
w_left = (window.screen.width - width)/2  
window.open('http://vk.com/share.php?url='+document.location.href+'&tltl='+tltl+'&cmg=1', 'shareSite','width=550px,height=268px,resizable=yes,scrollbars=yes,left='+w_left+',top='+w_top);}  
}  
</script>

<a href="javascript://" onclick="ShareToVk()">Поделиться Вконтакте</a>