  An Ore extension over a polynomial algebra F[x] is either a quantum plane, a
quantum Weyl algebra, or an infinite-dimensional unital associative algebra A_h
generated by elements x,y, which satisfy yx-xy = h, where h is in F[x]. When h
is nonzero, these algebras are subalgebras of the Weyl algebra A_1 and can be
viewed as differential operators with polynomial coefficients. In previous
work, we studied the structure of A_h and determined its automorphism group and
the subalgebra of invariants under the automorphism group. Here we determine
the irreducible A_h-modules. In a sequel to this paper, we completely describe
the derivations of A_h over any field.
