I would try to remove the card and reboot reinstall the drivers and setup your computer up with a manual ip therefore it should find your network and only your network.
It could also be some router saettings that need to be adjust such as portforwarding ,and disable wirrless network service too in windows xp it could be part of the disconnects since it always searching for a new network.
http://www.speedguide.net/read_articles.php?id=177
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