Permalink structure for Pages and Categories - where and how to?

[Gilbert]

Hi,

Busy experimenting with Goinggreen & Genesis for a site.
I have all posts accessible with the following permalink structure: /%postname%.htm.

Fine for all posts. However for categories or pages, I don't have the .htm displayed, which I would like to have.

See 'http://www.en.mon-anglais.com/english-courses' for an exemple of a page. Should I just name the permalink in the page 'http://www.en.mon-anglais.com/english-courses.htm', or is there a better and more general way to do?

I would like also to have the .htm extension for categories. Were should I do that? Should I do directly in the slug?