  We construct stable vector bundles on the space of symmetric forms of degree
d in n+1 variables which are equivariant for the action of SL_{n+1}(C), and
admit an equivariant free resolution of length 2. For n=1, we obtain new
examples of stable vector bundles of rank d-1 on P^d, which are moreover
equivariant for SL_2(C). The presentation matrix of these bundles attains
Westwick's upper bound for the dimension of vector spaces of matrices of
constant rank and fixed size.
