Where to despose of old hard drive

If you're really worried about no-one being able to access the data on it there are places you could go to get it securely shredded/destroyed (dunno where you'd find them in Ireland, and they'd generally deal more with bulk/business customers AFAIK).

Saving that there's some software you could get that overwrites it a set number of times with random and/or preset data (a *nix script that uses dd would pretty much serve this purpose if you happen to have a Linux installation around or anything).
Just a single over-write should be enough, no-one's ever demonstrated that they're able to recover data after an over-write, but it's apparently theoretically possible if you're worried about the FBA/NSA moreso than opportunistic criminals :P.

Other than that you could always just throw it in the Liffey >.>

The cheapest option if I was you OP, would be to dismantle it, and then take a drill to the platters. It would be a fun Saturday afternoon project. Once the platters are in a couple of pieces, dont throw them out altogether, but piece by piece.

You could pay someone to degauss it but its generally only done by companies and so it costs $$$. Maybe someone on here will volunteer to degauss it for you.