A template for an Integration test Plan, from Project Connections, usage restrictions apply.

Wikipedia has a good definition which includes top down and bottom up approaches in order to perform integration testing incrementally versus a big bang approach.

An interesting article form MSDN that positions integration testing in relation to Unit testing, that is Unit Testing without the use of Mock Objects. The example given is for SharePoint but this is a short and informative perspective on interface testing.

This Wikipedia entry gives an overview of test harnesses and mentions the strong relationship to automated testing. It would be possible to create a manual test harness as a set of screens that call components but typically these calls would be automated.