@Mike: You barely know this stuff. You can't be rusty :) Chern's 1951 Princeton notes say that for $M$ to embed in codimension $m$ we need that $\bar w_r = 0$, $r\ge m+1$, and $\bar p_k=0$, $2k\ge m+1$. (If I remember correctly, the bars mean the dual classes, i.e., the Poincaré duals of the dual Schubert cycles, but I'll have to review.)
Ah, right, these are formal inverses in the power series sense, but they do correspond to dual Schubert cycles.