The rip drive shoudl come with instructions, but basically it involves:
take apart halo, down to the point where you dismantle the gear train.
Remove a metal rod, replace with a longer one, reassemble.
It's not that hard, just make sure to take your time, work methodically, and dont lose any small bits.
Obviously the above is a lot easier if the Halo is ready for teh rip drive (has a small plastic plug in the bottom rather than needing a hole drilling/cutting in the shell)