More advanced training available online.
So, if you are beyond the basics on XML and are ready to get your hands dirty, this series of labs available on the MSDN site is very good. I especially end up sending people to Lab 15, which does a very good job of showing how InfoPath can reach into Active Directory and retrieve information based on a users's logon. I also reference Lab 14 quite a bit, which guides a user through setting up a custom task pane that changes the help displayed as the user tabs through the sections of a form. Very nice.