I recently build an HTPC (thanks to a little help from a few folks on these forums). Here's my setup: http://pcpartpicker.com/p/delU. The only things to add to this build are that I'm running Windows 7 Home Premium 64 bit, I have 8 GB of RAM, and I've got a Terk Antenna (INFO) plugged into a HD Homerun Dual (INFO).
I have installed almost nothing on it so I can keep it running as smoothly as possible. I even went overboard for my intent with the processor speed and graphics card because I was wanting it to be as smooth and future proof as possible. The only things I've installed on it since building it is XBMC (files stored locally for now), updated all the drivers, installed all the required utilities (ex. HD Homerun's utility, Silverlight, etc.), Hulu desktop and Microsoft Security Essentials. I also had CAT 6 run directly from the router to the HTPC through the attic yesterday and am experiencing no internet drops at all and get very good internet speed (consistently 30 down and 6 up).
The problem I'm having is that when I watch TV in WMC, no matter what channel, I'm getting stuttering of the video every 5-10 seconds, but only for a split second. It is very noticeable when watching something with a lot of action (like sports) or something with a ticker running on the bottom. I've scoured the internet for the past week trying to figure out what the cause might be and I can't seem to find an answer. I'm getting very, very good signal strength from the antenna (signal strength and signal quality in the high 90%s). I've tried hooking the antenna up directly to the HTPC and the same thing is happening. There is no problem with the audio, the video will just randomly stutter for a half second or so then jump forward to catch up.
Would anyone by any chance have any suggestions or know what my issue is? Is there some kind of codec that I don't have that I should download? I'm having no problem at all with XBMC, however I'm having a similar problem with internet video like Hulu or WatchESPN.com. I'm trying to cut the cord with DirecTv but having video that isn't smooth might potentially be a dealbreaker for me.