astv,
YES, you need BOTH. A good graphics card and a GREAT tuner card.
I'm only speaking from OTA (ATSC) tuners.... Pinnacle 800i PCI card. I don't do cable, but one day, I'll venture into the FTA satellite feeds. A very low income keeps me from going there.
Take a look at eBay for some of these cards as they're discontinued and Hauppauge bought out the Pinnacle tuners. These cards also do QAM for cable, but I can't attest to it's abilities or quality. This card really ROCKS for ATSC reception!
If anyone out there has some pointers to a great PCIe tuner....shout out, ok!
If you're looking for an External tuner.... HD Homerun. Hands down. Folks here swear by them, not AT them!
Graphics card? Any Nvidia board with a GeForce 9400 or better would work fine.
Welcome to the dark side of DVR's. We do pretty well here!