Design a form to respond to a workflow status : A very good resource for a starter in InfoPath Forms Development and workflow integration with Sharepoint.
Introducing of InfoPath Forms with Workflow : Explains theoretically what all are the workflows available in SharePoint 2007 and how they can be used with InfoPath Forms 2007. More theory than practical implementation.
Some other links:
How to develop workflow with InfoPath forms explained from a basic example to a complex one with code: Here u go
Ditto by from MSDN : Click here
Show the InfoPath form information submitted by user in the workflow task form so that the approver can view the form details and decide to either Approve or Reject: Click Here