help regarding installing python documentation

[N Sharmishta-in1769c]

Hi
I have installed the python 2.4 version and downloaded the HTML
documentation also.
But when I give the command help( ) in the IDLE command prompt and ' while '
,it says 
 
Sorry, topic and keyword documentation is not available because the Python
HTML documentation files could not be found.  If you have installed them,
please set the environment variable PYTHONDOCS to indicate their location.
 
I don't know how to set the variable PYTHONDOCS .kindly help .
 
Sharmishta

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