That's rather wearisome. Especially the recommendation to use thetrainline.com, which charges a booking fee that can be avoided by using the train operating companies' websites (even the ones that use thetrainline's engine!) I just went to East Midlands Train and had no hassle picking out a journey from London to Cork.
Do be aware that not all Irish stations are available for bookings (nor have they ever been). The National Rail system only includes major Intercity stations, and Boyle. You can normally book somewhere a stop or two later, but you're out of luck if you want to book somewhere between Ennis and Athenry, or Carrigtwohill or Midleton. There is a list of equivalencies in the National Fares Manual stating that if you want to go to X, use the fare to Y instead, but this requires the clerk to (a) know the list exists and (b) know how to issue a manual fare; most don't.
So what station were you trying to book to?