I have setup a Viewsonic VOT132 computer in our workplace which runs a Intel Atom 330 Dual Core 1.6Ghz CPU alongside a NVIDIA MCP7A-ION chipset. 

I have hooked up a AVerMedia Hybrid Volar HD USB Tuner to the computer in hope of picking up Freeview. 

I went down to my local Dick Smith and brought a Dick Smith branded HD Ready indoor antenna and put it on the window still. 

After the first scan all digital channels were picked up and I could watch them... sorta.

The video is very choppy with it lagging every 2-3 seconds. Looking at the CPU Monitor in the Task mananger of Windows 7 it shows the CPU's core's all cruising at around 10-20% optimization. 

The signal strength in the AverTV software fluctuates a lot more, it normally is higher than 50% but jumps around from 40% to 70%. 

Is this normal signal behavior or should it be fairly steady? And what would the minimum strength be to pickup a good signal?