Assuming that he has two feeds coming from the dish into the back of the DirecTivo, he needs to go into setup to ensure that the DirecTivo knows that two feeds are coming in. The way to check is to hit Tivo > Messages & Setup > System Information. Half way down the screen it should say:

DirecTV MultiSat
DVR Service Active
2 Tuners (Record/Record Enabled)

If it does not, he should hit: Left > Recorder & Phone Setup > Satellite Dish Setup > Repeat Satellite Dish Guided Setup. He needs to then follow the prompts and make sure to tell the DirecTivo that there are two inputs coming in.

If he does not have two coax cables coming from the dish to the DirecTivo, he can't do dual recordings.