[Distutils] buildout usage : a setup steps needs access to an installed package

[CP Hennessy]

Hi,
 I'm relatively new to buildout so this may be a stupid question :)

I'm trying to install nltk (Natural Language ToolKit) but it depends on 
PyYAML. So PyYAML is successfully installed as an egg before nltk. 

However nltk needs PyYAML during it's installation, but nltk does not have 
access to the PyYAML egg. 

How do I configure the buildout to give access to the PyYAML egg to the setup 
of nltk.

Thanks,
CPH