You say you modified the profile PATH to include the java /bin directory, but did it take? If you type $PATH at a command prompt, that ought to show you if the path is set properly.
The other possibilty is that you need to set your CLASSPATH environment variable to point to the java directory. You can test if this is the problem by using the -classpath flag when run javac:
javac -classpath=./:/path/to/java filename.java
Be sure to include the ./ bit, otherwise javac won't find the .java file you're trying to compile.