Setting Enviroment Variables

Hello,
I am curious if it is at all possible to set certain enviroment variables in Win9x machines. The issue deals with login scripts. I want these 9x machines to recognize the %username% & %os% variable. I don’t mind if I have to go around to each 9x to set this up. I have a couple of 9x machines, I would like to switch them to a different O/S but we need them for certain applications. Thanks for your help

Pete