Admin rights on local machine lost when

Am logging into Win NT Domain from my Win2k Professional system.

My login screen give 2 options.
1) Logon to Local Computer
2) Logon to Networks (Win NT Domain)

On my local computer & on Win NT i have Administrator rights.

but when i login to Win NT domain, I loose the Admin rights on local machine.

why is this happening ?? i wanted to do some changes to Tcp/IP properties. i had to logout from Win NT Domain & then login to local machine to perform this task. how do i preserve my Admin rights on both WIn NT Domain & as well as on my local Machine.