As far as cable card tuners, you can get Ceton internal 6 tuner model- http://cetoncorp.com/products/infinitv-6-pcie/
The other models are network tuners like the Ceton 6ETH or Silicondust HD Homerun Prime. There's a lot of info at http://www.thegreenbutton.tv/forums/index.php
You are in for quite a lot of work, I can tell you that. Putting together the PC hardware, OS, WMC, Tuner, and cable card pairing was the easy part. After that it took me 3 months to feel comfortable enough to turn in my rental boxes and sell my Tivo. And another few months to get WAF with different remotes and menus. I still have to tweak the series/scheduled recordings daily and be ready to reboot for unexpected tuner problems about once a month. Overall I am happy with the system and the savings.