I\'m somewhat new to WPF, so forgive me if this is trivial.
I have a panel set up like the following image suggest:
I would recommend that you use a UniformGrid control. From the linked page:
Provides a way to arrange content in a grid where all the cells in the grid have the same size.
Furthermore, it has a Columns property which enables you to set the number of columns that are in the grid.
You can find out more about the various Panels used in WPF from the Panels Overview page on MSDN.