Here's Link to the Queen Mary 2 homepage.
The Cunard Line also has the Queen Elizabeth 2, and the Queen Victoria will launch at the end of 2007. The website is very easy to use and organized to help travellers who access it.
Also, travel on a Freighter (cargo ship) is another option. Here's a link to that. It's an about.com link, so there are lots of other links on the page to click that have other information. http://studenttravel.about.com/od/boardaboat/a/boattravel.htm?terms=ireland+travel+agents
And Freighter World.
It looks like Freighters charge anywhere from $65.00 per day to $130.00 per day, so it's much cheaper than Cruise Ship travel. This is definitely the option I would take.
Good Luck and Have Fun on Your Trip.