Hi Paul, I think you are going to need to use full blown InfoPath and a forms library to do this. When you customize a SharePoint list using InfoPath you do not get to use all of the InfoPath features, just a subset that SharePoint lists support, a repeating structure is not one of them.
Additionally, to create new entries in a SharePoint list from InfoPath would require code which is not supported in the SharePoint List InfoPath customization.
Here is a good blog from the IP team about when to use a library via a list:
http://blogs.msdn.com/b/infopath/archive/2010/04/22/comparing-list-and-form-library-forms.aspx
One thing you might want to consider is to use a InfoPath from with code that creates mutliple rows in a SharePoint list. We have a tool called "qRules" that does just this and makes is very easy (without knowing any code) to map an InfoPath repeating section to a SharePoint list.
More details about qRules can be found here: http://www.qdabra.com/en/products/qRules.aspx and we offer a free trial version so you can test out how it works. The command you want is "Submit to SharePoint List" and you can watch a demo video here: http://www.screencast.com/t/NGQ4ZmFlM2Q
Ted