problem with IP thief

From: Olof Johansson (olofjoh_at_hotmail.com)
Date: 02/13/04 

Date: Fri, 13 Feb 2004 23:27:15 +0100

Hi people!
I'm having trouble with someone stealing my IP-number. Occasionally I
get the error message "A conflict has occurred for ip-number: <my ip>
with the system with hardware adress xx:xx:xx:xx:xx:xx" or something
like that (translated from swedish). I'm running win98, connected to the
internet on the university LAN. So I do have his/hers hardware address.
How can I find out his/hers IP from it? Then I figure I could also
locate him/her. Can this be done? Thanks in advance for all replies.
/Olof Johansson