This thread hasn't been posted in for more than a year, so let me jump in just in case nobody else is reading here anymore.
In Billings, you're looking at receiving six stations:
KTVQ-2 (2-1 CBS-HD, 2-2 CW-SD)
KHMT-4 (4-1 FOX-HD)
KSVI-6 (6-1 ABC-HD)
KULR-8 (8-1 NBC-HD, 8-2 Weather-SD)
K14IS-14 (14-1 Religion-SD)
KBGS-16 (16-1 PBS-HD, 16-2 Kids SD, 16-3 Create SD, 16-4 World SD, 16-5 Legislature SD)
KTVQ and KULR are on VHF, so you will need an antenna that will deal with both UHF and VHF.
Do you have any specific questions that I could attempt to answer?