I just learned something very important. I wish I had known how to do this a few years ago: How to get a white background using Photoshop CS4. Yes, I still have the old version of Photoshop. :-)
Anyway, check out this article from Tabletop Studio. It's so simple I could kick myself for not discovering this much sooner. :-) I'm so happy I found these instructions. Thank you to whomever wrote it. So simple and straight to the point.