Good advice Anthony; Visio is certainly better suited to structural and technical drawing than Paint. You'd wear yourself out doodling up little likenesses of "known shapes" that probably already exist in some plug-in for Visio. I didn't actually know why I spec'd Visio and Powerpoint when I bought my last PC, I had the full Pro suite PLUS at work, and didn't want to be hamstrung at home. I ended up swindling a deal on Visio, good thing too - Micro$oft's a little too proud of that product pricewise; ALONE Visio cost's more than an O/S.

Adam-san, the bottom line is that wherever you get/create your desired picture, you can put the frosting on the cake in Paint. If the resolution elves are on your side you could size pictures of a manufacturer's keypads and put them at the end of the wiring runs. You could take digital pictures of the actual lighting cans from an "ant's view" perspective, crop the ceiling away, and paste them at the end of their respective runs. If you're willing to tinker Paint can be manipulated in a lot of ways.

If you see a lighting diagram that you wish you'd drawn, but it's got other features that don't exist in your situation, or too many runs, you can take it into paint and start carving out the useful elements and storing them in a "toolbox" drawing. After some rehashing, cutting and pasting, and some expletives, you'll have spent more time for the same result as drawing it from scratch ; p

If you already had better programs you'd be a fool not to use them - If you get good enough with Paint and you're getting your desired result in reasonable time, you probably wouldn't feel the need to buy extra software.