Since you are using SharePoint the user can export to Excel right from the document library in SharePoint.
If you have repeating data in your form though you will need to use a web service to submit the from XML to a SQL DB to do reporting (and then export from SQL to Excel)
We have a tool called DBXL which can help you get the data into SQL. You can read more about it here: http://www.qdabra.com/en/products/DBXL.aspx
Ted