It depends on which fractions you want, what font you're using and what you
have your AutoCorrect set to in Word.
First, go to Tools -> Autocorrect -> Autoformat As You Type. Make sure the
option is checked to Replace as you type "Fractions...", about half-way down
the window. This means when you type "1/2" it will automatically change it to
the half-fraction character.
BUT this will only insert whatever fractions are included in the font you're
using. If your font doesn't include 3/4, for example, then typing 3/4 will
produce a blank space. For example, I like to use Optima as my default font,
but it doesn't contain any fractions and I have to go back and highlight that
blank space and select Arial to get the character to show. It's a pain, but
it gets the job done and I still get to use the font I prefer.
Hope that helps!
Jo