Alright... looks like I might have the go-ahead to build a HTPC for my parental units. But first... a few questions.
1) My dad's looking to consolidate the Cable Box, DVR, and Blu-Ray (they don't have a player yet) into this HTPC. What all is necessary to do this? TV Tuner + DVR software of some sort + Blu-Ray drive... anything else?
2) I've heard somewhere that a TV Tuner won't replace a Cable Box... what's up with that? If the Cable Box is still necessary, how would you hook it up to the HTPC in order to record shows and such?
A good TV tuner box comes with a IR sensor that takes control of the cable box. This allows the TV tuner to change channels as necessary. As far as I know only OEMs have access to cable cards which are needed if you want to replace your cable box.
Going from the wall -> cable box -> HTPC TV Tuner will give you all the channels that you currently subscribe to. The cable box is the tuner and you will need to use that to change channels. Many TV Tuner Cards come with a remote control and IR Blaster. The IR Blaster is just a receiver placed near your cable box receiver so you can use your TV Tuner Card's remote control to change channels (or just use the cable box remote control).
Going from the wall -> HTPC TV Tuner takes the cable box out of the loop, but now you are limited to whatever channels your cable company sends "in the clear" (or Clear QAM). What channels those are depends on your locale and cable company. In this scenario, the tuner card is the tuner and you'll use it (and the card's remote control) to change channels
Most (if not all) TV Tuner cards come with their own software for TV/DVR purposes, but I prefer to just use Windows built in software (XP MCE or Vista Home Premium/Ultimate).
I'm not overly familiar with Blu-Ray drives and the software required, but I've read accounts where the software that comes with the drive is an OEM version and not fully compatible with all Blu-Ray discs. Often people will need to purchase a full version of the software in order to have trouble free viewing of Blu-Ray discs.
What OS are you planning to use? I'm running Windows 7 RC on my HTPC right now, and everything worked out of the box, including my Hauppauge 2250 HD tuner that didn't play well with Vista or XP. The Media Center in Win7 takes care of all my DVR needs and is really easy to use.