Here are both input/outputs:
D:\>javac Usage: javac <options> <source files>
D:\>where javac INFO: Could not find files for the given pattern(s).
Apparently (as for Win 7) the implementation of where does not handle quotes (") poperly. It's probably better to remove them from your entire PATH environment variable (don't worry about spaces in this case).
after removing quotes:
What might be additionally misleading, is that where command could find properly java but failed with javac. It's because you might have JRE installed as well.