  We consider one-loop scalar and tensor integrals with an arbitrary number of
external legs relevant for multi-parton processes in massless theories. We
present a procedure to reduce N-point scalar functions with generic
4-dimensional external momenta to box integrals in (4-2\epsilon) dimensions. We
derive a formula valid for arbitrary N and give an explicit expression for N=6.
  Further a tensor reduction method for N-point tensor integrals is presented.
We prove that generically higher dimensional integrals contribute only to order
\epsilon for N>=5. The tensor reduction can be solved iteratively such that any
tensor integral is expressible in terms of scalar integrals. Explicit formulas
are given up to N=6.
