html form to XML response and reply

[Rapier]

I have a form that looks like this. Now a client has asked to convert this to a format that queries and sends response in XML. Can someone pint me to appropriate tutorial or example in PHP. There seems to be many ways of doing this\[code\]<form action="" method='post'><table><tr><td>User Number </td><td><input type='text' name='task_user_no' value='http://stackoverflow.com/questions/3800094/<?=$task_user_no?>'></td></tr><tr><td>Date </td><td><input type='text' name='task_date' value='http://stackoverflow.com/questions/3800094/<?=$task_date?>'> (YYYYMMDD)</td></tr><tr><td>From Time </td><td><input type='text' name='task_from_time' value='http://stackoverflow.com/questions/3800094/<?=$task_from_time?>'>(HHMM)</td></tr><tr><td>To Time </td><td><input type='text' name='task_to_time' value='http://stackoverflow.com/questions/3800094/<?=$task_to_time?>'>(HHMM)</td></tr><tr><td>Message </td><td><input type='text' name='task_message' value='http://stackoverflow.com/questions/3800094/<?=$task_message?>'></td></tr><tr><td>&nbsp;</td><td><input type='submit' value='http://stackoverflow.com/questions/3800094/submit' name='submit' ></td></tr></form>\[/code\]