I can't turn on my XP Security Center

My computer thinks it is part of a domain and that a network administrator
manages securty essentials. In turn I can not turn on Windows Firwall etc. I
also think this is why I am unable to connect to web pages other than those
in my browser? I tried to edit Group Policy (gpedit.msc) but that file could
not be found. I would like to achieve the ability to control my computer
rather than an invisible administrator.
I use Windows XP