[sliverstorm]

Well, there's a few possibilities. For example, if the ip address was associated with a DN, you could do a reverse-lookup and then do a whois.

[loboman]

Also he might know the friend's ip if the friend sent him an email.

[DanBC]

Knowing the IP is the easy bit.

Taking that IP and finding a street address is the tricky bit.

It can be done with court orders. (In England. I have no idea how Ireland does it.)

[loboman]

If he knows the friend ip, he knows that they both match (friend = troll).

[DanBC]

Ah yes, sorry. I missed that.