Hi Michael,
You should be able to use InfoPath 2003 with SharePoint 2007 workflows since it uses promoted properties from the forms (which was supported in InfoPath 2003) to manage the workflow states. There may be some features that aren't working for 2003 and in general, you're better off using InfoPath 2007 with SharePoint 2007.
To learn about SharePoint 2007 workflows, I would suggest looking for a lab on MSDN. Microsoft gave some good presentations at last year's TechEd conference in Orlando. You should search on those too.
Patrick Halstead
Project Manager at Qdabra