[ActiveDir] windows XP firewall problem

[tech]

Hello,   I have got SP 2(2055) for my windows XP. It seems that it has the new firewall. at first the firewall options were disabled and it was on and I could not chang it.   If I am disconnected from network I can change the firewall setting. I did turn it off then. but when I connect to my LAN again the firewall would be disabled and also would become on .   Does any one know how can I make it off and use it in LAN network?   It is strange I can disconnect network. turn off the firewall. then connect to network and join my domain. and then it works fine. but after 2 or 3 hours , the firewall will turn on and would be disable for changing?????????????????     Thanks in advance. Roseta