Advice on keying in accented characters

Using MS-Windows (e.g. Windows XP)

With a UK physical keyboard (one where the top row starts !"£$ rather than !@#$)

The secret is that you should use the control panel to set up Microsoft’s UK Extended keyboard.
(On an old computer, you’ll have to use instead the Irish keyboard - but don’t use Microsoft’s Gaelic keyboard, which isn’t actually nearly as good for typing Gaelic.)

Choose the following:

Start > Control Panel (or perhaps Start > Settings > Control Panel, depending on your computer)
Regional and Language Options
Languages
Details...

After this the fine detail gets a bit vague and depends on what you already have set up on your computer, but remember that what you are aiming for is:

Keyboard
  UK Extended

and that you can safely get rid of any other keyboards unless you know for sure yourself that you need them.

You’ll probably see something like:

EN English
  Keyboard
    United Kingdom

Click on the word “Keyboard” to select it, and then click “Add...”. Then from the dropdown menu under “Keyboard layout/IME” choose “UK Extended” and click OK. Then the simplest thing to do is to remove the “United Kindom” keyboard altogether because you don’t need it.

After that you should be able to get accents all the vowels, both upper and lower case, by pressing and releasing the grave-accent key on the keyboard (just left of the ‘1’ key) and then typing the vowel. This will work in any program whatsoever - Word, Excel, Notepad, Internet Explorer, Firefox, etc - and is very quick and easy.

As a bonus, the UK Extended keyboard also gives you the accents required for typing many other European languages - See this simulation.

If you have problems, give me a phone on 01471-888340 and I’ll try and talk you through it.

With a US physical keyboard (one where the top row starts !@#$ rather than !"£$)

The difference here is that you are aiming for Microsoft’s United States-International keyboard rather than Microsoft’s UK Extended keyboard. And also that you should retain the US keyboard rather than deleting it, because, while the United States-International keyboard is very useful for typing all sorts of accented characters, it makes it more awkward to type ordinary apostrophes and various other characters so you probably won’t want to use it all the time.