We construct stable vector bundles on the space P ((SCn+1)-C-d) of symmetric forms of degree d in n + 1 variables which are equivariant for the action of SLn+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 SL2(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.