How to work with dpkg --set-selections?

[Joachim Trinkwitz <upp105@ibm.rhrz.uni-bonn.de>]

I have saved my current package selections with `dpkg
--get-selections' and now I thought I could use this set to configure
a new workstation. Unfortunately, there seemed already to be some
preset selections from the installation procedure, which got merged
together with mine.

Is there any way to erase all previous selection before setting my own 
with `dpkg --set-selections'? Or how is the use of this parameter
thought?

To be a little bit more informative: I am trying to install Debian
with a homogeneous set of packages on 15 workstations. Which way is it
to do this best?

Greetings and thanks for your answers,
joachim