Lock down Windows XP

I am looking for XP tweaks or hacks that I can apply to my PC that will prevent software being pushed to my PC through a second party network. I need to be connected to the network to complete certain aspects of my job, but the software pushes they do messes things up. Of course I have repeatedly asked them to remove me from the list to push to, and they say they have, but I find proxy settings enabled and all sorts of other stuff changed on my PC when i come in. Is there a way I can block these pushes, short of disjoining the network every night when i leave?