The INI have an excellent free pack on moving back to Ireland.
Brent Irish Advisory Service produce a handy booklet called,
unsurprisingly, 'Moving to Ireland'. It details most of the
important information you might need to know (health, education,
housing, employment, etc.) about. You can obtain a copy from them at
296 Willesden Lane,
London NW2 5HW
Tel +44 81 459 6286
Fax +44 81 451 8865
There is also an FAQ for moving from the USA to UK which might help.