get current url into query string

Hello everyone, I am sorry to ask this again but earlier post was in a different subject. So I posted this again to get a better result. I have this markup:
<asp:HyperLink ID="HyperLink6" runat="server" NavigateUrl="javascript:;" onclick="window.open('http://www.facebook.com/sharer.php?u=' & Request.ServerVariables(""URL""),'mywin','left=20,top=20,width=550,height=500,toolbar=0,resizable=0');"> <img src="fshare.gif" /> </asp:HyperLink> I would like to set query string u to the current url. How can that be done?

Thanks. 



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