In Windows you can input character codes using the number keypad on the right of your keyboard.
Ensure the NumLock is on, hold down the (left) Alt key, and input a four digit code for the character using the keypad e.g.
Alt-0188 = �
Alt-0189 = �
Alt-0190 = �
To access ⅓ you can use the Character Map application found under Start → All Programs → Accessories → System Tools
This app also lists the Alt keystrokes needed to access characters other than the three examples above.