Unfortunately I know nothing about windows2000. I used to hack my schools 98 computers all of the time but... school protection software is slightly more advanced now.
If you cant access any programs in the start menu(like system properties, or system tools) and you cant get the task manager to come up... then, unless you can crack the admin code, there is nothing you can do.
I have an idea for cracking the admin code by the way...
I did it at my school. It was real fun.