The idea of changing the language settings is that you can then type characters quickly and easily (for example by pressing Alt+a for typing á).
This is a list that describes how to change the language settings for Windows XP.
Now you should see a keyboard icon at your task bar at the bottom. Click on this icon to switch to the United States International keyboard layout. This keyboard layout has a new key (AltGr) and 5 dead keys. The dead keys are explained below. An interactive diagram of this layout can be found in  (http://www.microsoft.com/globaldev/keyboards/kbdusx.htm).
The US International keyboard has two different Alt keys. The left Alt key continues to be the regular Alt key, normally associated with Windows menus. The right Alt key becomes what is called AltGr (or graphic Alt) key. This key lets you type very quickly special characters in Spanish and other languages by using AltGr and then typing a character from the list below.
Note: + indicate typing one key after the other. - is typing two keys at the same time.
á -> AltGr+a é -> AltGr+e í -> AltGr+i ó -> AltGr+o ú -> AltGr+u ü -> AltGr+y ñ -> AltGr+n
ç -> AltGr+, å -> AltGr+w
Á -> AltGr+Shift-a É -> AltGr+Shift-e Í -> AltGr+Shift-i Ó -> AltGr+Shift-o Ú -> AltGr+Shift-u Ü -> AltGr+Shift-y Ñ -> AltGr+Shift-n
Ç -> AltGr+Shift-, Ð -> AltGr+Shift-d
¿ -> AltGr+? ¡ -> AltGr+! « -> AltGr+[ Spaniards prefer «angular» quotes » -> AltGr+] Latin Americans prefer the “curly” ones ° -> AltGr+: Degree sign; ordinal sign, as in 4° año = cuarto año € -> AltGr+5 ¢ -> AltGr+Shift-c £ -> AltGr+$ ¥ -> AltGr+-
The US International keyboard has five dead keys. They add the symbol they have marked at the top of the following letter.
'+a = á; '+e = é; ... "+a = ä; ...; "+u = ü ~+a = ã; ~+n = ñ ^+a = â; ... `+a = à; ... '+Shift-a = Á; '+Shift+e = É; ... "+Shift-u = Ü; ... ~+Shift-n = Ñ; ...
To enter what's written on a dead key you need to add a space. ' followed by space generates an actual apostrophe.
Information on some other operation systems can be found here (http://www.studyspanish.com/accents/typing.htm).
You can type a special character by pressing and holding down the Alt button and then typing a number code on the number pad of your keyboard. The most frequently used characters have both a three-digit and a four-digit code. Less frequent characters (such as Á) have only a four-digit code. This page contains a good overview of special characters (http://www.starr.net/is/type/altnum.htm) for different languages
á -> Alt-160 or Alt-0224 ç -> Alt-135 or Alt-0231 é -> Alt-130 or Alt-0233 í -> Alt-161 or Alt-0237 ñ -> Alt-164 or Alt-0241 ó -> Alt-162 or Alt-0243 ú -> Alt-163 or Alt-0250 ü -> Alt-129 or Alt-0252
Á -> Alt-0193 Ç -> Alt-128 or Alt-0199 É -> Alt-144 or Alt-0201 Í -> Alt-0205 Ñ -> Alt-165 or Alt-0209 Ó -> Alt-0211 Ú -> Alt-0218 Ü -> Alt-154 or Alt-0220
¿ Alt-168 or Alt-0191 ¡ Alt-173 or Alt-0161
This method can be useful if you are just writing a short text (for example an e-mail) and don't have a computer where you can/want change language settings. Just try to pull up a web page or a document that contains the special characters and paste them into your text. For longer texts, however, this can become quite tedious.
If you are working with a text or you have the option to search for text and replace it with other text. This feature can be used to 'type' special characters. The idea is to mark a character for becoming a special character, for example typing ~a when you mean á. After you have written your text you replace marked characters (the ~a) with special characters (the á). Of course you have to either type in the Alt number code or paste the character, but the point is that you only have to do it once for the whole text and not for every single á that you want to type.
If you know a programming language that allows string processing you can automate the Search & Replace process by a computer program which automatically replaces all your marked characters with the appropriate special characters after you are done with typing your text.
Compared to Windows, typing Spanish characters on a Macintosh is relatively easy. So long as you are using a standard American or UK-style QWERTY keyboard, you may just use the following keyboard commands. (Note that you should release the Option (Opt) key before striking the second letter; for example, for á, hold down Option, strike E, release Option, strike A.)
One good way to practice typing Spanish characters on a Mac is to use the Key Caps program, which should be in the Utilities folder in the Applications folder. This simple program will show you what characters you can type next if you hold down the Option and/or Shift keys.
á -> Opt+E, A é -> Opt+E, E í -> Opt+E, I ó -> Opt+E, O ú -> Opt+E, U ü -> Opt+U, U ñ -> Opt+N, N
ç -> Opt+C å -> Opt+A
Á -> Opt+E, Shift+A É -> Opt+E, Shift+E Í -> Opt+E, Shift+I Ó -> Opt+E, Shift+O Ú -> Opt+E, Shift+U Ü -> Opt+U, Shift+U Ñ -> Opt+N, Shift+N
Ç -> Opt+Shift+C
¿ -> Opt+Shift+/ (forward slash; same key as ?) ¡ -> Opt+Shift+1 « -> Opt+\ (back slash; under the Delete key) » -> Opt+Shift+\ *Note that Spaniards prefer «angle quotes,» whereas Latin Americans prefer “curly quotes” as in English. ° -> Opt+Shift+8 Degree sign; ordinal sign, as in 4° año = cuarto año € -> Opt+Shift+2 ¢ -> Opt+4 £ -> Opt+3 ¥ -> Opt+Y
In KDE you can choose the international US keyboard layout. Go to Regional & Accessibility - Keyboard Layout in the KDE Control Center. Add the international US keyboard layout to your active layouts. With the flag icon in your taskbar you can now switch between different layouts.
Now you can type á by typing ' and then a:
'a á 'e é 'i í 'o ó 'u ú "u ü ~n ñ