You don't tell us where on your page the users select the specific "action param"
But maybe this example (a selectbox) can help you ??
Try This:
<script language="javascript">
function openWindow(url)
{
window.open(url, 'windowname','toolbar=yes, location=yes, directories=yes, status=yes, menubar=yes, resizable=yes, scrollbars=yes, top=0, left=0, height=600, width=800');
}
</script>
<form name="MyForm">
<SELECT style="width:275px" name="selectboxname" SIZE="1">
<OPTION value="none" selected>- Select a Link -</OPTION>
<OPTION style="color:#FF0000; background-color:#ffcc99" VALUE="
<OPTION style="color:green" VALUE="
<option value="">something goes <pre style="color:red">here</pre></option>
</SELECT><br><br>
<input type="submit" value="go for it" name="submit1" ONCLICK="javascript

penWindow(document.MyForm.selectboxname.options[document.MyForm.selectboxname.selectedIndex].value);">
</form>
Hope this helps,
Erik