I have 2000 Nissan xterra it just quit while I was drving it try starting it wouldn't start it sound like it out of gas but I have over 1/2 tank
so i wasn't too sure what it could be but i found a couple forums where people are having the same problems. you could check your fuel pump and your fuel filter.
http://www.clubxterra.org/forums/showthread.php?t=16754 -- check this out. Has your timing belt been replaced? If not and it's a 3.3L lets just hope it didn't break. If timing belt broke and it's the 3.3L you will have some major internal damage.
Search Nissan Xterra Questions
Nissan Xterra Experts