If it only lets you use OpenGL, try doing this to change it to Direct3D9 rendering system:
Go to your FeralHeart folder and open the ogre.cfg file. You should see: (as the first half)
Render System=OpenGL Rendering Subsystem
[OpenGL Rendering Subsystem]
Colour Depth=32
Display Frequency=N/A
FSAA=0
Full Screen=No
RTT Preferred Mode=FBO
VSync=No
VSync Interval=1
Video Mode=800 x 600
sRGB Gamma Conversion=No
What we want to change is the first row. All you have to do is change the Render System=OpenGL Rendering Subsystem to Render System=Direct3D9 Rendering Subsystem. Boot up FeralHeart, and it might possibly work. Please keep in mind that this mightn't be correct. Otherwise, I would suggest doing what Sarah said, (and what all the others said) because one of the map files might be the problem. Anyway, I'll keep this mind and sniff around to see if there is any other way to fix this.