Diablo is a series of two computer games, a third in developement. While the Game principle is the same there is only one common location in this games. In the first part you start in a small vilage called Tristram. Between Diablo and Diablo II Tristram is nearly completly destroyed (and some details rearranged). All inhabiants but one are dead, another one walks as undead through the town (unlike part 1, in which he allways stands at the same point).
Now about the music: The background music in Tristram is in both games exactly the same. Furthermore the Tristram theme plays a bit in the part 2 if you kill Diablo (the big endboss in diablo) who has destroyed Tristram between the games.
Here is it: