I am totally new to REST web services.I am in need to post some information to the REST web service and get the response which contains the detail of a job posting.The response and request is in xml format.I got some xml code from a developer and he said that he is using this xml to retrieve the details.

The xml code is

Code:
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ws="http://ws.mrted.com/">
    <soapenv:Header>
       <wsse:Security soapenv:mustUnderstand="1" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd">
          <wsse:UsernameToken wsu:Id="UsernameToken-1">
             <wsse:Username>PSHFK026203F3VB8MLO798NLD:guest:FO</wsse:Username>
             <wsse:Password Type="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-username-token-profile-1.0#PasswordText">guest</wsse:Password>
             <wsu:Created>2012-07-09T11:35:20.019Z</wsu:Created>
          </wsse:UsernameToken>
       </wsse:Security>
    </soapenv:Header>
    <soapenv:Body>
       <ws:getAdvertisementById>
          <ws:postingTargetId>6337</ws:postingTargetId>
          <ws:langCode>UK</ws:langCode>
       </ws:getAdvertisementById>
    </soapenv:Body>
 </soapenv:Envelope>
Now the question is,

1.How this code has been generated?

My php code is,

PHP Code:
$host = "https://apiurl?api_key=dabc4dvptajdnrhwnqsfxxxx";
$username = "guest";
$password = "guest";
$getjobdetail = '<?xml version="1.0" encoding="utf-8"?><getAdvertisementById>
              <postingTargetId>6337</postingTargetId>
              <langCode>UK</langCode>
           </getAdvertisementById>';

$headers = array();
$headers[] = 'Accept: application/xml';
$headers[] = 'Content-Type: application/xml; charset=UTF-8';       
$process = curl_init($host);
curl_setopt($process, CURLOPT_HTTPHEADER, $headers);
curl_setopt($process, CURLOPT_HEADER, 1);
curl_setopt($process, CURLOPT_USERPWD, $username . ":" . $password);
curl_setopt($process, CURLOPT_TIMEOUT, 30);
curl_setopt($process, CURLOPT_POST, 1);
curl_setopt($process, CURLOPT_POSTFIELDS, $getjobdetail);
curl_setopt($process, CURLOPT_RETURNTRANSFER, TRUE);
$return = curl_exec($process);
echo '<pre>';
print_r($return);
echo '</pre>';
curl_close($process);
2.Also for the username do I need to use

PHP Code:
$username 'PSHFK026203F3VB8MLO798NLD:guest:FO' 
or just

PHP Code:
$username 'guest'
Please suggest how should I proceed and if I am on the right path.Many thanks in advance.