Hi Jenz,
You could add a dual submit to the Web service first and then to SharePoint. Or, you could send the entire form as an xml string to the web service and have it archive it in a database or on SharePoint (our Qdabra DBXL accelerator web service does this). You can also use the merge option to display the data onload. That will require a custom xsl. We've done a couple of those before. If you only have 5-10 parameters, I'd say that's viable. Otherwise, I'd go with the roundtrip since then you have 100% datatype fidelity. Otherwise, the parameters coming out of the Web service will be slightly different and that could cause problems especially if you want to stream back something like an image attachment later.
I hope this helps!
Patrick Halstead
Project Manager at Qdabra