MPICH2 is available on Lattice and Knot. It is much the same as what you're using to using with mpich v1.
The main difference is instead of 'mpirun' the new command is 'mpiexec', and the flags are somewhat different.
In mpich v1, you would use
mpirun -np 8 -machinefile nodes ./a.out
while in v2, the terminology is almost the same
mpiexec -np 8 -f nodes ./a.out
i.e. notice the -machinefile flag is now '-f'