by plane or boat
As Ireland is on an island, I would think not.
West
Northern Ireland is part of the United Kingdom and on the island of Ireland. You can travel from the Republic of Ireland by driving across the border. The rest of the United Kingdom is across the Irish Sea, so you would travel by boat or plane to get to England, Scotland or Wales from Ireland.
There are some great websites that provide you with solid information on travel in Ireland. To name a few, you can visit Discover Ireland, Authentic Ireland and Lonely Planet.
Yes. A passport is not necessary to travel between Ireland and Britain.
I would check out cheaptickets.com or any of the airfare sites. Also look for "deals" on the travel sites. I would check out Ireland travel site also.
You would have to travel to France, and either get a ferry to Ireland from France, which is about 24 hours, or get a ferry from France to England and then another from England or Wales to Ireland.
Travel to Ireland
You can only travel from England to Ireland by air or sea.
If there were such a thing as leprechauns, they would probably not travel outside of Ireland. Fortunately, they're just a myth.
One could find a detailed map of Ireland at a local travel agents. This would be of the large fold out type. Alternatively one could find a map online such as the website Ireland Travel Expert.
No, you do not need any vaccines when you travel to Ireland.