Rok,

I don't want to sound rude as I could be missing something (been working for last 28hrs straight ) but isn't IP over a global network called the internet? Can you elaborate further as I'm sure I must be missing something obvious...

The fingerprinting concept is intriguing, but not applicable here, the figurative needle in a haystack. This technique is only viable if you can ensure a connection. I suppose a "call home" program could do this, but there's some many other ways of determining identity that don't require fingerprinting if you have access to install a phone home program.

I had my laptop stolen, and I almost recovered it, but not by my own sleuth work. The cops don't give a shit about your laptop, that's for sure. The funny thing about it, was that I had a bios level finger print reader with reciprocated encryption between the bios and harddrive. So basically, it was a 3K brick for the junkie who stole it.

Either way, if you're trying to pinpoint an IP without paying LoJack or something like that, you can always set a gmail notifier or desktop to start on computer start and save the username and pwd. Gmail gives you a log of recent activity at the bottom of their webmail interface, detailing the type of access and the IP location. You'll still have to provide the police with the IP, but it's a start. I'd also suggest a webcam monitoring service running in the bg and sending snapshots etc.

I have previously seen some javascript that would pull the mac address, but you would have to get the user to browse to your website and it would have to be a windows machine browsing with IE.
http://www.devarticles.com/c/a/JavaScript/Advanced-JavaScript-with-Internet-Explorer-Retrieving-Networking-Configuration-Information/1/