In Windows go to Start - All programs - Accessories - System Tools - Character Map.
Select the font that you are using and click on the character that you need. You can then copy it to your clipboard and insert it wherever you need it.
Also, in the bottom right corner, for many characters, you will see "Keystroke" and "a" followed by a number.
This is useful for frequently used characters, if you keep a note of the numbers it is simply a matter, without going to the Character Map page, of holding down the Alt key and typing the number. e.g. Alt+130 gives é or Alt+0128 gives € the Euro sign, try it!
It is also possible to build whole words before saving to the clipboard.