Sitemap in footer with all different pages

Dear WP users,

For one of my projects I’ll be needing a sitemap in my footerbar. I’ve been checking out the wp_list_pages tag for this but I’m having a problem:

I’d like to have multiple lists of page and subpages horizontal outlined.

Sitemap:

mainpage mainpage2 mainpage3
subpage subpage subpage
subpage subpage subpage
subpage subpage subpage

How is this possible with wp_list_pages?

Thanks in advance!
Robin.

(ps: Don’t get my point of view? Take a look at the design at the bottom:
http://www.steptomac.com/index2.html)