Windows Xp has a firewall you need did to disable it. i beleave and the punting/boot every one should stop.
if the windows xp don't know them it will disconnect them from your server. (Panther has this info i beleave)
i not too clear on this firewall to much but do remember something about it.
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about skin's a bet info:
also if they are try to use skin and it not enable they get punted out automatic (this is normal)