Charlie which version of Outlook are you using?

In Outlook 2003 and older you can select a default document template to use for your emails. Outlook 2003, 2002, and 2000 work stand alone to do this, however older versions do it indirectly through Word.

I have not tried using an html document template with Outlook 2007. I'm sure it can do it, just haven't wanted to wade through the "ribbon" to find where the feature is located.