It's not on Volume one; I think tupogirl is talking about two different things, and just phrased it in a way that makes it look like she's talking about the
Young Indiana Jones and the Curse of the Jackal /
Spring Break Adventure music being on the first CD.
The Indy Wiki has the tracklist
here; no Mexico stuff, as you can see.
I wish it were otherwise.
For some reason the Wiki doesn't yet have info on the other three volumes - I'll have to rectify that myself, I guess. In the meantime, though, for the record, these are all the episodes represented on the four officially-released volumes for
The Young Indiana Jones Chronicles (note that they're not in any particular order on the CDs - all the music from a given episode is all together, but the episodes are mixed around in no particular order on the various CDs):
"Vienna, November 1908"
"British East Africa, September 1909"
"Peking, March 1910"
"Princeton, February 1916"
"Ireland, April 1916"
"London, May 1916"
"Verdun, September 1916"
"Paris, October 1916"
"
Young Indiana Jones and the Phantom Train of Doom"
"German East Africa, December 1916"
"The Congo, January 1917"
"Barcelona, May 1917"
"Northern Italy, June 1918"
"
Young Indiana Jones and the Mystery of the Blues"
"
Young Indiana Jones and the Scandal of 1920"
... plus two versions of the show's Main Title theme, which is the closest they get to having music from the Mexico segment (pretty close, though, actually, since there's that scene when Indy's on horseback chasing after the guy with the stolen dresses).
That said, Curt Sobel, the composer for the episode "Transylvania, January 1918," released a promo CD of his complete score for that episode, and there's also a 2-disc Laurence Rosenthal promo that has music from various projects of his, including
Young Indy, and it does have some
Young Indy music not available on the four volumes released by Varèse Sarabande, but not from that particular episode (
Young Indiana Jones and the Curse of the Jackal), though that's one he did score.