Because it was installed as a domain, there is too much to change. Just reload the OS and be sure to answer this question as a workgroup. See link -> http://www.blackviper.com/os-install-guides/windows-xp-professional-install-guide/
It's at step 29 where you must be careful.
And no, there is no supported method to change this after install.
I have a former work computer that was part of a network at the office that runs on WindowsXp Professional. I can't access the internet at home as both aol and IE8 are unable to detect the connectivity device that's installed on this computer (Realtek ethernet NIC). I removed this computer from it's former domain and assigned it to a work group thinking this might be the problem but it hasn't helped. Are there any other configuration adjustments I need to make to gain internet access? Thanks, Wade