SOLDIERX.COM Nobody Can Stop Information Insemination

Bit of a weird request here:

I have noticed an unsecured wireless network in my area that still has the default admin username & password. Naturally i logged in and nosed around just for giggles.

What i want to do is trace the exact location of this router and notify it's owners that it is unsecure and that they could really get fucked over BUT i can't seem to lock it down to to an exact address. I reckon the AP is in my street and (funnily enough) i have a contact number for the user of the AP (ISP username is their telephone number). They are ex-directory.

There are 3 minds I'm in:

1 is to be a bastard, leech the hell oout of their network, max out thier usage etc etc just because
2 is to "do the right thing" and tell them so they can sort it out
3 is to do 2 but do it for them and charge.

I've got the landline number and the router MAC, is there anything i can use to pinpoint exactly which house it is?

Any help?

Note: I am in the UK, not US.