Blog sitemap AND static-pages sitemap?

I have an existing static website, to which I have added a Blog page (http://example.com/wordpress). I used Google XML Sitemap Generator to generate a sitemap . . . it generates a sitemap, in the http://example.com/wordpress directory, which includes the blog pages but nothing else.

I added the home-page of my site (to “additional pages”), but it refuses to add that (maybe because I have a sitemap there already?, or because the Blog is on a subdirectory?).

So . . . is it good to have two sitemaps, one for the static pages and one for the Blog?? If not, how can I get a plugin to do what’s best?

Chris