I notice you are getting ATI Card. ATI has some disadvantages when it comes to onboard H264 decoding using DVB-T in NZ.
There is a bug with ATI decoding interlaced H264 DVB-T siginal (TV3,C4,TVNZ6+7,TVNZ Sports extra) using onboard decoding. You may need to use software decoding, however your processor is fast enough to do software decoding if you can't get hardware decoding. You only decode the H264 signal when you display the TV on your monitor, not when you are recording. So you would not get increased cpu useage when recording, just when viewing TV.
You should have no problems getting hardware accleration on non-interlaced H264/VC1 content with blu-ray & 720p/1080p H264 movies you download.