Help please, how do I find out where a message came from (ISP?)

Help please. I am trying to track down the originating computer of a message as the person is also a stalker. I can get "message source" but this gives a bunch of numbers, so how do I tell which is the originating place? Here's one example, with personal stuff deleted(me=me, myprovider is my provider, nasty is sender, * is senders provider, my mail gets sent through postini to viruscheck before coming on to me). Thank you so much.

rom - Wed Dec 07 10:01:20 2005
X-Account-Key: account2
X-UIDL: d]E"!Lp-!!"TB"!HoL"!
X-Mozilla-Status: 0011
X-Mozilla-Status2: 00000000
Return-path: <nasty@*.net>
Envelope-to: me@myprovider.com
Delivery-date: Wed, 07 Dec 2005 00:52:59 -0800
Received: from pop3.myprovider.com (<208.200.248.2> helo=myprovider3.myprovider.com)
by myprovider3.myprovider.com with esmtp (Exim 4.43)
id 1Ejv2p-0005px-H7
for me@myprovider.com; Wed, 07 Dec 2005 00:52:59 -0800
Received: from exprod6mx163.postini.com (<64.18.1.163> helo=psmtp.com)
by myprovider3.myprovider.com with smtp (Exim 4.43)
id 1Ejv2p-0005pi-3z
for me@myprovider.com; Wed, 07 Dec 2005 00:52:59 -0800
Received: from source (<209.165.130.12>) by exprod6mx163.postini.com (<64.18.5.10>) with SMTP;
Wed, 07 Dec 2005 00:52:58 PST
Received: from <10.0.1.2> (<65.74.32.217>)
by msgmmp-2.*.net (Sun Java System Messaging Server 6.2-3.03 (built Jun 27
2005)) with ESMTP id <0IR400128E0062I0@msgmmp-2.*.net> for
me@myprovider.com; Tue, 06 Dec 2005 23:52:53 -0900 (AKST)
Date: Tue, 06 Dec 2005 23:52:51 -0900
From: Nasty <nasty@*.net>
Subject: Re:
In-reply-to: <4395C6EE.3090305@olypen.com>
To: <me@myprovider.com>
Message-id: <115A5D39-E1C7-499C-ACB6-65E561B0C7B6@gci.net>
MIME-version: 1.0
X-Mailer: Apple Mail (2.746.2)
Content-type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
Content-transfer-encoding: 7BIT
References: <E744FC2C-A37C-4307-9657-1D5DA5230188@gci.net>
<4395C6EE.3090305@myprovider.com>
X-pstn-levels: (S:99.90000/99.90000 R:95.9108 P:95.9108 M:96.8122 C:99.7951 )
X-pstn-settings: 4 (1.5000:1.5000) s gt3 gt2 gt1 r p m c
X-pstn-addresses: from <nasty@*.net> forward (user good) <3591/147>
X-OLYPEN-SPF: pass
X-UIDL: d]E"!Lp-!!"TB"!HoL"!

10.0.1.2 - is a reserved domain (for private networks), doesn't tell you anything.
Reverse DNS on the next three (65.74.32.217,64.18.5.10,209.165.130.12) gives:

217.32.74.65.in-addr.arpa name = 217-32-74-65.gci.net.
12.130.165.209.in-addr.arpa name = msgmmp-2.gci.net.
10.5.18.64.in-addr.arpa name = *.mail5.psmtp.com.

So, it seems to be coming from someplace named "gci.net", which is here:

http://gci.net/

You might consider contacting them about Mr. Nasty, but be polite, this is speculative.

or have to check with gci. I think it is coming from not a dialup, but something that is continuously on (DSL, satellite, some such) so I was hoping someone could help me figure out the more specific #'s, or perhaps we might end up blocking all gci from our website.. Thank you for the input and we may just contact gci.

You would have to talk to GCI, since they control things from there on in.
It should be easy to set up an IP filter (in a firewall, for gci) or a mail filter for Mr. Nasty.
You can lawyer GCI about Mr. Nasty too, but that takes work and money.
Of course there are other things as well, but we won't go into that, we could get in trouble ourselves.

peace

to your ISP to let them know gci refuses to police its own customers.

I would first filter out this person's address. Some mail clients will let you bounce the mail. Mail.app in OSX allows you to. I don't know about the others.