To pass your VoiceXML variable to ASP, you would have to <submit> your variable to an ASP page. Here's some example IVR code that should help you do this:
<?xml version="1.0"?>
<vxml version="2.0">
<form>
<field name="customerid" type="digits">
<prompt>
Please enter your customer identification number using your keypad.
</prompt>
</field>
<field name="age" type="digits?minlength=1;maxlength=2">
<prompt>
Please enter your age using your keypad.
</prompt>
</field>
<block>
<prompt> Please wait while we process your information. </prompt>
<submit namelist="customerid age" next="http://mightyserver.com/submit.aspx"/>
</block>
</form>
</vxml>
<%Response.ContentType = "text/xml"%>
<?xml version="1.0"?>
<%
dim customerid
dim age
customerid = Request.QueryString("customerid")
age = Request.QueryString("age")
%>
<vxml version="2.0">
<form>
<block>
<prompt> Your customer identification number is <%Response.Write(customerid)%>. </prompt>
<prompt> Your age is <%Response.Write(age)%>. </prompt>
</block>
</form>
</vxml>