Sketchy has written a fantastic, and very detailed article on the possibilities of using good old Microsoft Excel... as a level editor. It's really informative and well worth a read. Included is a source file to assist you.
Comments from Sketchy:
"Making a game tile-based is a great way to cut down on the amount of graphics you need to produce, and also speeds up level creation. However, it's almost always necessary to make a custom map editor - fine if you're working on a big project, but very tedious if you just want to make a few quick maps to test an engine.
One solution I've found, is to use Microsoft Excel as a map editor. By using Excel's "conditional formatting", it's possible to make quite a functional map editor - and it's even possible to replace a lot of your MMF2 map loading code with just a few formulae in Excel."
Click here to read the article and comment on it