Paul,
I would add to the advice that Cathy listed to ask your radiation oncologist about amifostine, a medication that can sometimes preserve salivary gland function, although nausea appears to be a strong adverse effect.

You didn't mention if you would be receiving chemotherapy with your radiation. Recent studies seems to show that this is a more effective treatment. See, for example, in the news section:
http://www.oralcancerfoundation.org/news/story.asp?newsId=826
and
http://www.oralcancerfoundation.org/news/story.asp?newsId=809
and
http://www.oralcancerfoundation.org/news/story.asp?newsId=768

Good luck with your consultation and best wishes for a successful treatment. - Sheldon