The Unreal Technology Page has undergone an update, by way of a True-Type Font Importing Tutorial by Epic's Jack Porter (thanks PlanetUnreal). Apparently Unreal mod makers can use any True Type font in their mods (although it should be pointed out that many popular fonts are not public domain, and therfore cannot be freely distributed). Here are the details:

The TTF importer allows you to convert a Windows true-type font of a particular size into an Unreal font which you can then use to draw in-game text. The Unreal engine now has support for rendering anti-aliased fonts, and the TTF importer allows you to import the anti-aliasing from a Windows font.

Unreal has had the ability to import true-type fonts for use in-game since version 224, although there was a bug in the 224 font importer code which meant all the fonts you imported ended up as MS Sans Serif. Be sure you're using Unreal 225f or later, or you may have problems.