first you should have your script code at the very beginning of the page between the <head> and </head> tags.
<head>
<script language="Javascript">
<!--
function click()
{
top.window.opener.location.replace('../Forms/PetrolReport2.asp?EmpView=<%= Request("UserID"

%>&Status=<%= Request("Status"

%>&ToDate=<%=Request("ToDate"

%>&FromDate=<%= Request("FromDate"

%>');
}
//-->
</script>
then the form should be like this.
<form name="myform" action="../Forms/SendMailForm.asp" method="post" onSubmit="javascript:click();">
<table bgcolor= "cccccc" style="width:500px;" cellspacing="0" cellpadding="0" border="1">
<table style="width:500px;" cellspacing="0" cellpadding="0" border="0">
<tr>
<td><input type="button" class="button" name="close" value="Close" onclick="window.close()" style="width:100"></td>
//take out the onclick event handler
<td><div align="right"><input type="submit" class="button" name="submit" style="width:115" value="Approve / Decline >"></div></td>
</tr>
</table>
</form>
I haven't tested this code yet but this is the idea.