Jeff,
if this chart is made with the wizard, I don't think so. The wizard usually creates a crosstab query automatically from the data and groupings that you input. I wonder though, if you might be able to write your own crosstab, sort it the way you want it, and simply specify that dataset as the source when you make the chart through the wizard.
I don't know if that will work as I've never tried it, but it's definately worth a shot if you don't find anything else.