CPU at 100% during Over-the-Air HD digital broadcast

[mike400hp]

My SageTV Server:

Hardware:
Asus A8N-VM CSM Motherboard
Athlon64 3200+ 2GHz
512MB RAM
Asus GeForce 7600 GS 256MB RAM
Creative Labs X-Fi XtremeGamer
Hauppauge WinTV-HVR-1600
Western Digital 500GB 7200rpm SATA

Software:
Windows XP Pro
SageTV 6.1.45
nVidia PureVideo

The problem:
I use the HVR-1600 to view/capture basic cable from my provider. The goal of upgrading to the HVR-1600 was to be able to view Over-the-Air HD boardcast as well as tune the basic cable channels that are available. Tuning and watching basic cable channels works great. However, when I connect my HD capable antenna and try to "View" the dectected channels in the program list setup, the CPU jumps to 100% useage. The channels will come in, but since the CPU is maxed out they are jerky and frames are dropped. I think that my hardware should be able to handle the HD feed, but it appears not to be able to. Maybe I do not have some kind of "Hardware" transcoding happening and the CPU is being forced to process everything?? Does anyone have any idea?