Chemistry help please?? :)

i'm terrible in chem, and need some help balancing equations and whatnot..

solid ammonium nitrate decomposes to produce gaseous nitrogen and water vapor.

if anyone could pleaseee balance that for me and include the phases i'd really appreciate it!!
(and maybe even a brief explanation of how you get the right answer so i can learn how)
Thanks in advance!

I think the problem is that the products listed are not complete: either oxygen of nitrous oxide must be included.

Set up an equation with just the reactants and products:
NH4NO3 -----------> N2 + H2O
You cannot balance this equation. If N2O is a product then:
NH4NO3 -----------> N2O + H2O (balance hydrogen)
NH4NO3 -----------> N2O + 2 H2O (balanced)
If oxygen is one of the products, then
NH4NO3 -----------> N2 + H2O + O2 (balance hydrogen)
NH4NO3 -----------> N2 + 2 H2O + O2 (Balance O, not enough on left)
2 NH4NO3 -----------> N2 + 2 H2O + O2 (rebalance H)
2 NH4NO3 -----------> N2 + 4 H2O + O2 (balance N)
2 NH4NO3 -----------> 2 N2 + 4 H2O + O2 (balanced)

You had trouble because the list products was incomplete!

2NH4NO3 (s) --> 2N2(g) + O2(g) + 4H2O(g)

The decomposition of ammonium nitrate has to produce oxygen gas as well. If it didn't the reaction would be impossible to balance.