One idea to get SOAP call examples is use the debug window in the admin UI. Just login to the admin UI with ?debug=3 and it will dump each soap call. The setpasswordrequest should look like:
Code:
<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
<soap:Header>
<context xmlns="urn:zimbra">
<sessionId id="1718"/>
<authToken>
AUTH TOKEN
</authToken>
</context>
</soap:Header>
<soap:Body>
<SetPasswordRequest xmlns="urn:zimbraAdmin">
<id>
ACCOUNT ID
</id>
<newPassword>
NEWPASS
</newPassword>
</SetPasswordRequest>
</soap:Body>
</soap:Envelope>