Well I'm late to this thread but since this is one of my favorite topics figured I'd chime in.
There is a LOT of great info here already so I don't want to rehash that. I have a few options that I'd like to share thou.
First of all if you don't want to spend at least a small amount of time tweaking stick with the cable company box or get a Tivo. Now to me either of those options would be like going back to a nice SDTV after having a HDTV, at least thats how I feel. But it's true, with any HTPC you will likely have at least SOME tweaking to do. If that doesn't scare you away then read on.
Right now there are many choices and ways to go about getting/building a HTPC. I've tried many but settled on XP MCE because I liked the design and how it just all works so I can speak to that better than the rest. I am eagerly awaiting the Vista version of MCE mainly because of the mentioned CableCard and HDCP support. Those two things are a REQUIREMENT for HTPC and PC support of HD type content in the future. I am not aware of how Apple will be addressing that issue (I'm sure they will however) but right now it doesn't look so good for Linux. In a nutshell what I'm suggesting is you may want to sit back and give this another few months to hash out because going thru the trouble of buying/building an XP MCE or something similar will be a futile effort since you will need Vista anyway for all the things that are going to matter now and in the future (HDTV from cable and Blu-ray/HD-DVD).
I do currently get HD on my MCE box using an OTA (over the air) tuner with antenna. I don't get any cable channels in HD that way, and yes it's a pain (because of the antenna) to setup but at least I have some HD content (for free).
I love my current setup, HDTV, AVR, MCE box. That's it. Having everything in one box (HTPC) to me is a very big perk. Everything in it works so seemlessly together and I've really gotten used to it being that way. Being able to put movies *online* and with a visual represention that is searchable is outstanding. Say I realize I forgot to set a show to record, I can open a webbrowser up and go to my box and tell it to record that show. The DVR functionality kills any cable company box I've been around. I've heard Tivo is better than the cable company boxes but I can't speak to them since I haven't used one (just my ReplayTV from back in the day). Having all my music on demand is something else I'd never be willing to give up. Browsing or searching for something to listen to with the album art on the screen is what I've come to expect now. I could go on and on.
I know I've listed all the reasons to get a HTPC now but with cablecard support and HDCP just a few months away in Vista I would sit back and wait till early next year and see how everything shakes out. If you have a spare PC thats calling your name, I'd say go for it now to get you hands dirty a bit but don't spend too much money right now if you care about HD.
