Quick & quiet for home entertainment cntr on the cheap- good choice?

Seeking quick and quiet for home entertainment center (internet, photo editing, VHS to DVD conversions, watching Blu-Ray, Streaming Music and Video) and general use. As I am a novice, I have been looking at commercial builds to see what they use and then making modifications. The following combination in an mATX case can be purchased already built for $650. Hope to build better for less. Please rate my build- good choice?

Specs:
AMD Phenom 9650 Quad (considered the 905e but concerned it is too new to have proven itself / may exceed my budget)
780G chipset Motherboard- The already built system uses MSI MS-7548 (appears to be an OEM exclusive board). Considering either the ASRock A790GMH or the Gigabyte GAMA78GPM-UD2H or GA790X-UD40 (with the later, will add a discrete graphics card)
ATI HD4850 (the built system used HD4350)
8 GB DDR2 SDRAM
750 7200 RPM SATA HD
Hauppauge TV Tuner with Remote Control Media Cntr (Open to recommendations on the one that is best for recording TV while viewing other content)
Vista Home Premium
DVD Burner and Blu-Ray Player
450 or 500 Watt PS (the built system uses 300 Watt PS)
Still deciding on a case, want one less than 9" tall

Look forward to your feedback.

Thank you for taking the time to provide feedback and for your recommendations. Any thoughts on the ASRock A790GMH versus the Gigabyte GAMA78GPM-UD2H or GA790X-UD40 Motherboard with or without the ATI HD4850?

Thanks again.