import problem in zope

I installed zope under windows and found a problem when import addition
modules - iHotfix and itools. When place itools in python's library
path, site-packages, import works fine. When place itools in
zope-instance's library path, /zope-instance/lib/python, it seems the
the import only work partially, for examlple, only partial attributes
and methods are imported. Someone say that this porblem will disapear in
linux box, I will try it. But now, my question is what the difference
between site-packages and zope instance library path is. Counld anyone
help me.

Thanks.

Jack