Well I can't give any comments on the Xterra, but I have a Pathfinder which is double-din. If the Xterras are too (which I'm pretty sure they are) then the install is pretty much cake. The hardest part I had was squeezing both mounting brackets (3rd party HU and Empeg) together in the space.
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One of the last MK2's from SonicBlue... Blue/60gig S/N: 030103111