[Your URL]?id=your_value
Using PHP:
<INPUT TYPE=submit value=\"$id\">
Using Javascript something like:
Code:
id = location.href.substring(location.href.lastIndexOf(' '),location.href.lastIndexOf('id=')+3);
would find the field value for id
then use a javascript write to the value into the form:
Code:
<input type=submit value="<script language="JavaScript">document.write(id);</script>">