Ignoring the VBA part, I'm not sure you can do that at all - you can set a background for a sheet, and you can set a background for a shape, but I have never seen a way to add a cell background image in excel, and a quick google doesn't show up any way either - though there are a couple of queries from people trying to, they all have the "shape" solution.
I don't think you can do exactly what you want, but certainly you need to find out if it is possible at all: I'd try looking for a "ExcelProject" type site (if there is one): there is a QA facility on this one:
http://www.excel-formulas.com/[
^] which may help you. I have no idea if they charge or not - I've never used them.