[pdftex] include-directory

[Stueker, Dirk]

Hi,
I am am searching for a command to define an include directory for 
used packages. My directory structure like this:

-+--- Include-Dir (.sty-Files)
 +--- Document1
 +--- Document2
 +--- Document3

Document1, 2 and 3 all need the same .sty-Files and I do not want to
replicate the files to every directory.

Thanks in advance!
Dirk