How do you replace the front differential on a Subaru?

You have to remove the entire transmission, and the tranny is in 3 parts. Back of it is the transfer case which houses the center differential (viscus unit), the middle section is the gearbox itself, and the front section (bell housing) is the front differential. All of these sections can be separated and replaced individually.

As for specifics on step-by-step instructions, that's beyond the scope of my patience and technical aspirations of WikiAnswers unfortunately.