The JackCompiler runs from the command line (cmd.exe), not from a desktop shortcut or clicking on JackCompiler.bat in Explorer.
You need to add your nand2tetris\tools directory to the PATH environment variable so that Windows can find the batch file.
On Windows 7, right-click "Computer" icon and select Properties. Go to the "Advanced tab" and click "Environment Variables..."
Scroll down in the System variables list and select "Path" and click the "Edit..." button and add your nand2tetris\tools directory, followed by a ';', to the beginning of the path. Close all the dialogs and start a new Cmd window. Type "path" and you should see your directory
C:\Users\marka>path
PATH=d:\TECS\tools;c:\usr\binw;c:\python3.4;c:\python2.7; ... etc.
C:\Users\marka>
Now you should be able to use JackCompiler from the command line without needing to type the full path name
C:\Users\marka>d:
D:\>cd tecs\projects\09\Reflect
D:\TECS\projects\09\Reflect>dir *.vm
Volume in drive D is SHAREDDATA
Volume Serial Number is CCFB-1BE4
Directory of D:\TECS\projects\09\Reflect
File Not Found
D:\TECS\projects\09\Reflect>JackCompiler
Compiling "D:\TECS\projects\09\Reflect"
D:\TECS\projects\09\Reflect>dir *.vm
Volume in drive D is SHAREDDATA
Volume Serial Number is CCFB-1BE4
Directory of D:\TECS\projects\09\Reflect
04/10/2015 07:18 PM 5,197 Ball.vm
04/10/2015 07:18 PM 6,481 Game.vm
04/10/2015 07:18 PM 6,975 Main.vm
04/10/2015 07:18 PM 3,687 Mirrors.vm
04/10/2015 07:18 PM 864 Random.vm
04/10/2015 07:18 PM 2,659 Target.vm
6 File(s) 25,863 bytes
0 Dir(s) 12,094,406,656 bytes free
D:\TECS\projects\09\Reflect>JackCompiler /?
Usage:
JackCompiler Compiles all .jack files in the current
working directory.
JackCompiler DIRECTORY Compiles all .jack files in DIRECTORY.
JackCompiler FILE.jack Compiles FILE.jack to FILE.vm.
D:\TECS>
--Mark