1) Find/track the spacecraft
2) Steer antennae to follow the spacecraft
3) Create transmitter and receiver hardware capable of communicating with the spacecraft's radio equipment (perhaps software radios).
4) Write software capable of handling the transmit and receive protocols.
5) Write software that captures the state of the spacecraft.
6) Write software that can control the spacecraft.
7) Decide where the spacecraft should go (hopefully, if we were to reestablish communications, perhaps NASA would help with the physics).
I think the bulk of the project consists of performing the research required to actually "speak the spacecraft's language". Fortunately, this part of the project is most conducive to crowd-sourcing and collaboration.