My friend Rafal Kolanski and I decided one night to put our gigabit network cards to the test and measure how quickly a user-space program could generate packets and how many would be discarded before the destination's NIC would receive them. Therefore we wrote a small Linux program to complement my Broadcast Flooder, which I had previously written to test other aspects of my network.
Incoming and outgoing bandwidths were measured using the Windows Task Manager and Performance Monitor (for more detailed statistics), and gkrellm and conky on Linux.
Both programs (simple packet generators) are included here, with source code. If you want to perform more hardcore testing with Linux, you should use kernel-mode the packet generator (but with care!).
(Can you find the reference to a certain MC in the hammer source code?)