R help - Jul 2004 - Interpretation of poly(x, y, degree=2) coefficients

Does anyone know of a function that turns the coefficients of

lm( y~ poly(x1 , x2, degree=2))

into something that can be interpreted easily.  I was think along the
lines of the matrix representation of quadratic forms:

(x-mu)'A(x-mu) +k ,

and finding the eigenvectors/values of A, and the vector mu, but anything
that allows me to visualise a contour plot would be great.

Thanks

Simon Bond