Due to the high level of heterogeneity in a computational Grid, designing a runtime system for such computing infrastructure is extremely challenging, for example regarding the ability to exploit transparently and efficiently various networking technologies. Programming a computational Grid often requires the use of several communication paradigms (RPC, RMI, DSM, Message passing) that have to share these networking resources. This paper presents the first step towards a runtime system that allows efficient communication for various communication-oriented middlewares. We introduce a CORBA implementation that reaches 240 MB/s, which is as far as we know the best CORBA performance. Thus, CORBA can be as efficient as MPI on high performance networks. Moreover, we show that different communication middlewares, like CORBA and MPI, can efficiently co-habit within the same runtime system taking full benefit of various networking resources (SAN to WAN).