  Negative dimensional integration method (NDIM) seems to be a very promising
technique for evaluating massless and/or massive Feynman diagrams. It is unique
in the sense that the method simultaneously gives solutions in different
regions of external momenta. Moreover, it is a technique whereby the
difficulties associated with performing parametric integrals --- the standard
approach --- are transferred to a simpler solving of a system of linear
algebraic equations. Employing this method, we calculate a massless two-loop
three point vertex with all the external legs off-shell. Then NDIM approach
allows us to obtain twenty-one distinct new power series representations for
the integral in question. In order to verify the correctness of our results, we
consider five particular cases where either two of the external legs are put
on-shell, or one of them amputated or one exponent of the propagators is set to
zero, and compare our results thus obtained with the ones calculated with
standard methods in positive dimension.
