Why not take it back to the shop, and tell the guy you either want a refund or for him to fix your computer without using pirated software? I'd still call the cops and rat him out to Microsoft, but may as well give him an opportunity to do the right thing in the end.
You have a perfectly good Vista license that you were using before you took your laptop to this guy, so why should you have to pay him for the privilege of having to pay for additional software that he installed without permission?
Recently my laptop suddenly stopped working (it wouldn't boot). Took it to a PC shop and the guy told me I needed Windows reinstalled (I was running Vista). He did this for me, but installed 7 (Home Premium) instead. Anyway after a couple of weeks it started asking me for my activation key, and after a little digging on another forum I realised I'd been sold an unlicensed copy of Windows.
So I've got about a week to get a new activation key. My question is: do I need to buy this, at £110...
or can I get away with buying this, at £90?
Bearing in mind I don't actually need to install anything, just to use the genuine license which is included in the purchase.