Submit XML Via POST

[hiritek]

Hi,

Im trying to setup a form that a user adds data into, and then for that information to be submitted via XML to another website:

This is a demo form:

<form method="POST" action="https://www/xmlrequesttest.php">
<input type="hidden" name="xmlrequest" value="<XML/>”>
<input type="submit" name="submit" value="Submit">
</form>

And i need the XML to look like:

<AVAILABILITYREQUEST>
<USERNAME>test</USERNAME>
<PASSWORD>test01</PASSWORD>
<USERDATA>0394298888</USERDATA>
</AVAILABILITYREQUEST>

I dont understand how to link the xml into the form....?