Hi Ian,
Are you saying that you have a bunch of XMLs and you want to import them another XML that you are using for reporting?
If you haven't created the InfoPath forms, you could start from the XSD for the FusionChart Gantt but I'm guessing it's too abstract.
Best bet would be to translate XML from your InfoPath forms into your reporting format. You can use XSLT to do this.
Qdabra has a new tool coming available that will let you batch extract XML from SharePoint form libraries and create Excel reports. That probably won't do the trick for you. We have a lot of experience doing XSLT and conversions. We could definitely convert the forms for you but it would involve some paid support. Let us know if you would like to engage by emailing Support at Qdabra dot com.