permanently change wireless network connections

Everytime I turn on my HP xe2000 Laptop with XP, the it automatically
connects to a different company in our office building's wireless network.
I have changed the order of preferred networks, removed all other networks,
changed from 'automatic' to manual, and still, everytime I start up the
computer I have to manually make it find our network (our router is 5 feet
from the laptop). I can always get on our network this way, but it doesn't
seem like it should be that difficult to get it to start by finding our
network. I have the settings so that it should 'find our network when in
range".
suggestions?
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BLW