Welcome to LQ.
The leach + leach_c code doesn't work with ns-2.35 :
At least not with the latest code update (by @exidus).
The good news : You can have as many versions of ns2 as you want,
installed at the same time. But do never add any *PATH text to .bashrc.
Writing a new ns2 protocol : You will need some experience with ns2.
And : The code is c++, tcl, otcl.