He would need to give Virgin a call on 150 from his landline or 0345 454 1111 from any other phone to add a TV subscription to his package. He will be sent a TiVo box or a V6 box if he pays an upfront fee.
The lowest TV package Virgin offer is called "Player TV". The standard price for Player TV, VIVID 100 broadband + phone is £48 per month. For an extra £7 he could get "Mix TV" which would give him quite a lot of extra channels. For best results, he should use the "thinking of leaving us" option as that's the customer service team. As he's adding a new service they may apply some discount.
See here for a list of channels included in the Player TV package.