In WINDOWS XP
Go to 'Start' ==> 'Control Panel' ==> 'Regional and Language Options' ==> 'Languages' ==>Details
Below 'Installed Services' you'll see the list of languages your computer is already set up for.
If you see 'IR' and 'Irish(Ireland)' there - you're set up. Close everything down and go to below for detailed instructions on 'Using this keyboard'.
If you don't see 'IR' and 'Irish(Ireland)' - you're going to have to install it. Don't worry - it's really not scary.
Click 'Add' button ==> click on 'input language' dropdown and scroll down until you find 'Irish' ==> click on it to highlight it and move to keyboard layout IME
This will probably have 'Irish' in it. You can leave this, OR select 'Gaelic' from this dropdown. As far as I can see, you get the same output from both.
CLICK apply - OK - OK and close down to leave your control panel.
Now you're ready to start - almost.
To create the à ì è ò ù - you just hit the ¬` button (just above 'tab') on your keyboard, then a e i o or u and you get the vowel with the accent over it. Peasy!