A good question on the smallpicture-web list.
How can I use a Google Web Font in my Fargo website?
There are probably a few ways to do it, but imho the easiest is to add the font includes and new style declarations in a
<%customStylesScripts%> glossary entry. This is included in every template, after all the other styles and scripts, in the head section. So you can override anything, in theory, by putting it in that glossary entry.
Here's an example site that illustrates.
Here's the OPML source for the site.