Web services & soap headers...

i have an c# windows service which is calling a web service, i need to be calling a web service provided by a 3rd party which is fine. i have added a reference to it and can see all the functions which i need to call. my problem is that before i call this i need to call their authentication service which will provide me with a security token to use during that session. they have sent me an example of the SOAP message which needs to be sent, an the information needs to be sent in the soap:header .....which is where i get my problem, how do i specify information for this SOAP header.

any pointing in the write direction would be great thanks!!!!

here is the example SOAP message :

<soapenv:Envelope xmlns:soapenv="" xmlns:wsse="">
<soapenv:Header>
<wsse:Security>
<wsse:UsernameToken>
<wsse:Username>test</wsse:Username>
<wsse:Password>1234</wsse:Password>
</wsse:UsernameToken>
</wsse:Security>
</soapenv:Header>
<soapenv:Body>
</soapenv:Body>
</soapenv:Envelope>

thanx for this post