Definitely replace both engine mounts, if one is torn or otherwise noticeably bad, the other one is bad as well. The tranny mount is a simple job. The engine mounts aren't overly difficult, but as Thomaspin stated you do have to use caution when starting the bolts or risk crossthreading.
Be sure to loosen the fan shroud to allow a little more lift when you start to jack up the engine. All of the hoses should have enough flex to leave them in place during the procedure.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.