If you use the Character Map, as suggested by Imfeduptoo (which is also available from the Start menu, if you're a mouse user; Start-Programs-System Tools - Character Map), when you select any character it will show the key code required in the bottom corner. This is the code to type in (in this case ALT + 0190) as described by Bleeper. This means that once you've looked up a character, you can note down or remember the code number to save using the Character map for common symbols.
Worth mentioning, the ALT + code only works on a numeric keypad and not the number keys along the top row of the keyboard. This means it might not be available if you use a laptop.