One of my friends shipped a lot of his books (like a huge burlap sack of them) to Ireland by boat/ocean book freight or whatever it's called. Only cost him something like 72 bucks. I don't know who provides the service, but it can be done.
On a different note, has anyone been overweight with baggage in Heathrow? I came to the Heathrow Aer Lingus counter, bound for Cork, and was way over for weight. The agent actually prompted me for a bribe. He handed me back my passport, told me to go to the washroom and put 100 quid inside and return to the counter (I was told my overage fees would have been more than double that). And I have heard the same from other NAmerican students coming over. I wonder if it's the same guy and how much he's clearing above his salary.