I got it all setup last night and scanned the channels properly and actually watched some live TV through Myth.
I did notice what appeared to be buffering problems and when I exited out of Myth, there were errors related to that, something to the effect of "buffering pause", but it was already midnight and I was beat.
I am going to move the HTPC into the living room and get it hooked up to the TV and see what my signal is like out there via the RCA indoor antenna I have:
RCA Amplified Flat-Panel HDTV Antenna
With a flat-panel design, this HDTV antenna will provide you with improved reception for your favorite high-definition channels without taking up too much space.
Compatible with off-air HDTV broadcasts
25dB amplification with low noise filter improves reception of weak signals and optimizes picture clarity
Patented T-Bar UHF element is specifically tuned to receive signals in the UHF spectrum (channels 14 and up)
Adjustable gain control helps fine-tune channels
It was just something the local Bestbuy had in stock for me to test with, but I am sure it's not the best indoor antenna there is, but I really don't want to go crawling in my attic to mount anything either.
So tonight it's a matter of figuring out my buffering problem whether its related to signal or hardware resources, but I really don't think is hardware bound as the CPU is a 2.4ghz P4, 1Gb Ram, etc.