Keith Fuller has posted a detailed run-down of what is in the recently released Soldier of Fortune SDK, which includes everything you should need to make mods, maps or models for Raven's gory first person shooter. According to Keith, Raven have "included for your perusal the source code to the game dll as well as the player dll, comprising everything you'll need to handle player inventory and weapons, create your own deathmatch gameplay modes, and produce all manner of wacky conversions."
The SDK also includes Raven's own version of the QERadiant level editor, map compile utils, config files for the in-game tools, model export plug-ins, sample files, and documentation for most of the goodies. For the full details, as well as information on how to compile the source code, read Keith's designer's diary over on SoFCenter. You can grab the SDK here.