feifong - are you just changing out the differential or the ENTIRE REAREND HOUSING? The differential is only the 'guts' of the rear end located in the housing -- to change it you have to remove the rear cover, remove the carrier bearing caps and pull it out. You need to measure backlash before you remove it -- because with a different diff, you may need to shim it differently to get the proper spacing so the gear mesh is the same.
If you're replacing the whole housing -- MUCH easier in terms of mechanics. As others have said -- you'll likely need the proper brake line fittings/hoses, and the correct proportioning valve. The last piece is REAL important. If the front to rear balance isn't correct, you can end up with a car that either locks it's rears too soon (a BIG problem) or one that isn't taking any advantage of those new discs you'll have back there.