Can you bring up the "text Services and Input languages"?
In Windows XP
On the bottom of the screen, you might see "EN" or "US", if you see that, right click & open "Settings".. If not then open the control panel (start -> control panel), then open "Regional and Language Options". Click onthe "languages" tab, then click "Details..." button.
Separate window opens, in the settings tab, choose "English (Ireland) - Irish" in the drop down list.
That *should* sort you out. Again, the above if for XP, not too sure what it is for Vista (but should be similar)