  The nonsingular variety G_T parametrizes all graded ideals I of R=k[x,y] for
which the Hilbert function H(R/I)=T. The variety G_T has a natural cellular
decomposition: each cell V(E) corresponds to a monomial ideal E for which
H(R/E)=T. Given a monomial ideal E, the quotient R/E has a basis of monomials
in the shape of a partition P(E), having "diagonal lengths" T. The dimension of
the cell V(E) is the number of difference one hooks of P(E).
  We show that G_T is birational to a certain product SGrass(T) of small
Grassman varieties, and that over the complexes, the birational map induces an
isomorphism of homology groups, but not usually an isomorphism of rings. We
determine the homology ring) when T=(1,2,...,d-1,d,...,d,1). This G(T) is the
desingularisation of the d-secant bundle Sec(d,j) of the degree-j rational
normal curve, We determine the classes of the pullbacks of the higher singular
loci of Sec(d,j). We also use the ring H*(G_T) to determine the number of
ideals satisfying an intersection of ramification conditions at different
points of P^1.
  A main tool is a combinatorial "hook code" for the partition P(E), that gives
the image of the cell V(E) in SGrass(T).
