The problem with a cheap OEM PC or *cough* Atom *cough* isn't the cpu processing power per se, but the GPU. You haven't said it, but I'm guessing it is HD? You'd be looking at choppy playback on a HDTV. Also, what OS would it be? Windows? Then a AMD 785G + HD 4200 onboard video will do just fine. If Linux, you want a discreet nivida gpu like GeForce GT 220.
For netflix, you don't need a TV tuner card. For cable, it's best to consult with your cable company about recording shows on computers. It may not be doable. i.e. encrypted cable signals.
Yep, the Harmony would work with a pc or any pc, but you need the driver software & the bundled USB infrared receiver. You'd plug the receiver in a pc, install & set up the driver.
$300 can buy the HTPC minus a tv tuner card:
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SAMSUNG CD/DVD Burner Black SATA Model SH-S223C
SAMSUNG CD/DVD Burner Black SATA Model SH-S223C - OEM
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$19.99
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APEX DM-387 Black Steel MicroATX Slim Case Computer Case 275W Power Supply
APEX DM-387 Black Steel MicroATX Slim Case Computer Case 275W Power Supply - Retail
Item #: N82E16811154087
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$44.99
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SAMSUNG Spinpoint F3 HD502HJ 500GB 7200 RPM SATA 3.0Gb/s 3.5
SAMSUNG Spinpoint F3 HD502HJ 500GB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive
Item #: N82E16822152181
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$54.99
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MSI 785GM-E51 AM3 AMD 785G HDMI Micro ATX AMD Motherboard
MSI 785GM-E51 AM3 AMD 785G HDMI Micro ATX AMD Motherboard - Retail
Item #: N82E16813130247
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* 2 year: $16.99
$79.99
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G.SKILL 2GB 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600) Desktop Memory Model F3-10600CL9S-2GBNT
G.SKILL 2GB 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600) Desktop Memory Model F3-10600CL9S-2GBNT - Retail
Item #: N82E16820231252
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$49.99
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AMD Sempron 140 Sargas 2.7GHz Socket AM3 45W Single-Core Processor Model SDX140HBGQBOX
AMD Sempron 140 Sargas 2.7GHz Socket AM3 45W Single-Core Processor Model SDX140HBGQBOX - Retail
Item #: N82E16819103698
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$32.99
Subtotal: $282.94
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