[XPelargos]

Okay, here's what I did. Go to steamapps/common/sourcesdk/bin/ep1/bin and open GameConfig.

Copy/paste this into it, changing your account name of course.

Also remove (x86) if you have 64bit architecture.

"Configs"
{
	"Games"
	{
		"Fortress Forever"
		{
			"GameDir"		"c:\program files (x86)\steam\steamapps\sourcemods\FortressForever"
			"hammer"
			{
				"GameData0"		"c:\program files (x86)\steam\steamapps\sourcemods\FortressForever\ff_base.fgd"
				"GameData1"		"c:\program files (x86)\steam\steamapps\sourcemods\FortressForever\fortressforever.fgd"
				"TextureFormat"		"5"
				"MapFormat"		"4"
				"DefaultTextureScale"		"0.250000"
				"DefaultLightmapScale"		"16"
				"DefaultSolidEntity"		"func_detail"
				"DefaultPointEntity"		"info_ff_script"
				"BSP"		"c:\program files (x86)\steam\steamapps\common\sourcesdk\bin\ep1\bin\vbsp.exe"
				"Vis"		"c:\program files (x86)\steam\steamapps\common\sourcesdk\bin\ep1\bin\vvis.exe"
				"Light"		"c:\program files (x86)\steam\steamapps\common\sourcesdk\bin\ep1\bin\vrad.exe"
				"GameExeDir"		"c:\program files (x86)\steam\steamapps\sourcemods\FortressForever"
				"MapDir"		"c:\program files (x86)\steam\steamapps\sourcemods\FortressForever\maps\vmf"
				"BSPDir"		"c:\program files (x86)\steam\steamapps\sourcemods\FortressForever\maps"
				"CordonTexture"		"tools/toolsskybox"
				"MaterialExcludeCount"		"0"
			}
		}
	}
	"SDKVersion"		"3"
}

oaties forgot to add "common" to the path file which is how steampipe has changed the SDK location. Then, do what alex did.

1. Open SourceSDK
2. "Refresh SDK Content" (because we changed the gameconfig)
3. "Edit Game Configurations"
4. Click "Add".
5. Type "Fortress Forever" under 'Name'
6. Add the Directory of the Fortress Forever folder. Select 'Ok'
7. Launch Hammer