If you're talking about character shadows, the best solution I can offer is that you check out the link to my shadow system below. It's not free, but writing a system to cast shadows is anything but easy. There are some free solutions out there, but they don't do a very good job. (Either they don't optimize the shaodw rendering, or they cast shadows onto "cloth" meshes which they then try to wrap around the underlying geometry in the world, which doesn't work that well.)
If you're talking Doom 3, everything casts shadows, shadows, then forget it. Can't be done in Blitz 3D.
If you're talking Doom 3, everything casts shadows, shadows, then forget it. Can't be done in Blitz 3D.