Without knowing your itinerary, it's pretty hard to give an informed answer, but if the object is just to spend time in those towns/cities, then you would probably be quite content to NOT have a car.

All three locations have compact, conjested Centers that are easily walkable and are less than car friendly.  Parking is tough to find, and/or expensive.  Both Galway and Kilkenney are serviced by train to/from Dublin and there are substansial discounts available for tickets purchased on-line (as late as the night before!).  Galway and Dublin both offer a plethora of options for daytours -- you will be spoilt for choice, should you be so inclined --

Mary Gibbon's Newgrange/Tara or any number of Glendalough/Powerscourt from Dublin and the Aran Islands and/or Kylemore and Connemara from Galway are just a few examples that come to mind ...

BUT ... if the plan is to range, far and wide afield from those towns (and you are adverse to group day tours), then a car is ESSENTIAL. 

Realize this probably does NOT help MUCH, but ...

Needing or not needing a car to tour in Ireland is a VERY personal and subjective call.  I could NOT servive even a week, going without, but my interests (for activities AND locations) make for some pretty 'Off-The-Beaten-Path' wandering.

Bob

Tony,

From the info you have given I think you will be fine without a car. As Bob says both Kilkenny and Galway are connected to Dublin by train. My only advice would be to contact the Dublin tourist office in advance for them to find out if the Galway tours are still going. They may have a reduced schedule at the end of Oct. That may determine which days you will be there.

Have a fabulous trip and let us know how it goes.

Michele

You can get to Belfast via train, as well. It is a very pleasant experience. They also have bus tours from Belfast to the Giant's Causeway. Again. check with the Tourist Information folk in Belfast to determine which tours are still operating and their schedules.

Another thought, have you looked at Paddywagon tours? They offer both "structured" tours, a term loosely used, and hop-on/off tours which allow you to explore a town at your leisure and then grab the next Paddywagon ambling by. They originate in Dublin and have their own hostels which are fantastic.

Slan Beo,

Bit

Tony,

Glad to hear you have a plan and are ready to go. Have fun!

Michele