Ways to identify a machine

From: Matt (mattloude_at_hotmail.com)
Date: 07/31/04 

Date: Sat, 31 Jul 2004 00:00:11 -0700

What are different ways to identify a computer? by computer name? ip
address?

For example, when I create different id to logon a service, it can identify
me as the
same user even I use different id.

any ideas? any ways that dont allow the computer is not identified?

please advise. thanks!!