Is there a way to set a default cateogry for any new posts?

I am working on getting one of the mail 2 MT scripts working, but as my site displays the categories in the pages, I'd like to define a default category for use with any post which came in via e-mail (or anywhere else for that matter).

Alternatively, does anyone have a pointer to some perl code for assigning a category to a post via the XML-RPC API?

Thanks much