Stupid Question: Front Diff vs. Transfer Case(?)

[jaypete1]

2000 4.4 125k - At about 90k, the stealer replaced my front CV axles. But they messed up the installation, and within 40 miles the lub leaked out of the front differential and it failed (crunch, grind,...). The stealer (eventually) took the blame and replaced the front diff for $0 (the bill read $3,200). Now, my indie tells me the "front 2-piece driveshaft" is wearing out and should be replaced soon. When coasting through a parking lot at ~15mph, then applying power I get a distinct "clink", thus his diagnosis. Anyway, with all of the recent posts about driveshaft & transfer case problems, my uneducated questions are:
1) is the "front diff" the same as the "transfer case"?
2) should I be replacing the front driveshaft sooner rather than later to avoid issued with the transfer case?