  We consider the crystal structure of the level zero extremal weight modules
$V(\lambda)$ using the crystal base of the quantum affine algebra constructed
by Beck, Chari and Pressley. This approach yields an explicit form for the U^-
extremal weight vectors in each connected component of the crystal of
$V(\lambda)$, which are given as Schur functions in the imaginary root vectors.
We use this fact to demonstrate Kashiwara's conjectures regarding the crystal
structure of $V(\lambda)$.
