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You won't be able to use the InfiniteScrollArea widget in Alfresco 4.2 because it is part of the external Aikau project that is only available for use in Community 5.0.d and Enterprise 5.0.1 onwards.
We don't actually have the ability to have fixed headers on lists at the moment, but there is a more generic FixedHeaderFooter widget which (as the name suggests) allows you to have a layout with a fixed position header and/or footer with a central section that scrolls. You could place a list inside the central section and have an empty list in the header.
This wouldn't be an optimal solution - an option that is always available is to raise a feature request as an issue on the Aikau project or better yet submit a pull request that provides the capabilities that you want added. Contributions will be accepted as long as they meet the acceptance criteria and the unit tests pass.