GLSL shaders in any case. I think Luther Blisset was working on normal maps, but that was during 2238 era, probably 2-3 years ago... Check out some of the old threads around here, he was posting on our old forum (now archived, maybe stickied someplace).
From the designer point of view, anything as big as Fallout sprites/objects and up to 2 or 3 times in size shall not profit visually from normal maps. In other words it is depending on your plans.
About GLSL: In the current FOnline SDK the shadow for 3D characters is drawn this way, coded by Cvet. Unfortunately there is no source code for it, you would have to make something on your own or ask on IRC.