You should have 2 listings of each channel in the guide. The first one is the HD version of the local channel and it will have the station call letters. The second one is the SD version and it usually just has your locality initials with the channel number next to it.
For example, here in LA if I were to look at our local CBS (channel 2). The HD version would be listed first and it will be listed as 2 KCBS in the guide. The SD version would be second and it will be listed as 2 LA2 in the guide. NBC HD (channel 4) would be 4 KNBC and NBC SD would be 4 LA4.