  Formulae are provided to express any two-loop scalar integral with arbitrary
masses and arbitrary external momenta in terms of an integral of one fairly
simple function or of its derivatives. Such integrals can be calculated
numerically with high precision. Good agreement is found with known analytical
expressions of specific two--loop diagrams. To prove the effectiveness of these
techniques, the two--loop selfenergy of the Higgs boson to order $(g^{2}
\frac{m_{H}^{2}}{m_{W}^{2}})^{2}$ is calculated, and the correctness of the
result is checked by using the unitarity of the S matrix. This result allows
one to disentangle the leading corrections to the shape of the Higgs resonance,
and to derive a perturbative bound of $\sim$1.2 TeV on the mass of the Higgs
boson.
