Note: Don't confuse the ALT key with the ALT GR key, both of which can normally be found on the bottom row of the keyboard. The ALT GR key is used to produce the third character found on certain buttons of the keyboard.
To type any of these special characters in Word or any other word processor press the ALT key (and keep it pressed) then type the number shown for the character one digit after another on the number pad to the right of your keyboard. When you've done that release the ALT key and the special character should appear. Thus to get the inverted question mark character ¿ just press the ALT key and type 168.
Can't find your character? Go to Start - Programs - Accessories - System Tools and finally Character Map. There you will find a complete table of unusual characters. Copy it from there and paste it in your text.