Special thanks to Instinctual from Instinctual for providing code that enabled me to have my site switch between 3-column and 2-column modes and to Norma from Rightminddesigns for providing code that enabled me to have a fixed-width home page and variable width all other pages.
Both of you have been immensely helpful, as are the X-Cart forums in general.
You can see the almost-completely-tweaked results here:
www.bitsbytescomputer.com/store
John