I need to add a link to a page that will submit a request to a
differnt URL, but after it's done it should refresh the current page
(the page where the link was).  I can control content of the respose,
the only catch is that I have no way of knowing the URL of the
original page.

This will redirect to the second page with the current URL on the
query string.  The second page will then be able to get the original
URL off of the query string and redirect back.

Here is the code for the original page:

<script type="text/javascript">
  function Go( url ) {
    // Get the current url and escape it (URL encode)
    var currUrl = escape( window.location.href );
    
    // Go to your new page
    window.location.href = url + '?returnAddress=' + currUrl; 
  }
</script>

<a href="javascript:Go( 'http://someurl.com/secondpage.html' );">Click Me!</a>

it also can get the url of the request page in the pape where the link redirect to.
For Example,In VBScript of ASP,the command is
request.servervariables("http_referer").