How to assign default layout to site in SP?

System

In SitePub 7.2.1 (or any before), how does one assign one of the fixed layouts (3 column fixed, 3 column liquid) to the whole site when creating a site?

I've figured out the copying of the layouts into the site's workarea to make them available when creating a page within the site, but I can't get the layout type to show the 2 extra fixed layouts when creating a site.

I know you're supposed to choose the Default HTML as the type, after which all of the available layouts are supposed to show up as options.

Help?