how to list all installed modules

[harryos]

hi
Is there a way to list all the installed modules in my python
installation.I recently installed pygame and when i tried to import it
like
>>import pygame
it complained that no such module was found.I can see the pygame
directory in F:\Python25\Lib\site-packages in my machine,but am unable
to import the module.So I was wondering if there is a way to list all
the installed modules

any help much appreciated
thanks
harry