What type of TV channels are you using? Analog tuner, digital tuner, HDPVR or CableCard? The process varies slight for each.
If you're using a digital tuner, the general approach is to go to the Settings->Channel screen, and double click a channel. It'll now be showing you the channel details, including it's EPG source. You can switch that EPG Source to Schedules Direct, select the lineup and mapping, then hit ok. After this first channel, you can either do the rest of the channels the same way, or you can use the Bulk Map to change a lot of channels in one go.
