Generate XML (via input) and pass to server for verification - repost

On our site we need to modify an existing script to generate an XML based on the inputs provided by the user and pass to an external site via soap and get a response. If the response is pass, the existing script will continue. If it is fail, it will alert and stop. I can provide full examples of how this should work. It should be simple. XML is generated based on user input on certain fields, passed to external server upon submit, and pass or fail will determine if script continues. Thanks.