Did you install oracle client apart from oracle datase(server) software?let us know what oracle software and os you installed ?
Set ORACLE_HOME and PATH correctly and then try to execute.. post your ORACLE_HOME and PATH
Fallow the below steps:
> cd C:\Oracle\oracle10g\product\11.2.0\client\BIN -- > this path many be different in your case.
If you need to automate this than you need to set the env variables.