The CRYSTAL environment variable should be in the instructions somewhere... it is just an environment variable that's set to be the absolute pathname to your Crystal Space installation.
We probably need to create a sticky for that topic
The errors you're getting means that it can't load the given plugins. So they were either a) not compiled or b) not found. If your environment variables aren't set, then (b) would be your problem. If you have problems while compiling or running the configure script, (a) would be the cause.