I'm sitting here at work, practically bubbling with excitement over the prospect of my latest endeavor: MythTV.
I've been looking into an open source PVR ever since I first started reading about people hacking their Tivos years ago. Since Tivo is Linux based, customizing the system is only as hard as getting access to it. Naturally it's not easy to do that, especially on a Series-1 no-network-access machine, but not impossible. That eventually led to smart people writing open source PVR projects such as Freevo and MythTV. I don't want to start a debate on which of these is better--that would be pointless. After researching both projects MythTV felt like the right one for me, so that's what I'll do.
I initially tried to price what sounded like a decent but low-cost system by just picking components out of the air. That started approaching 2 grand so I started searching on the web. O'Reilly did a review of how to build a quiet PVR, but it, too, was well over $1000.
The cost put me off for a while until a friend who has a MythTV box said I was shooting way too high if I was spending more than $500. I did a search today for "mythtv less than $500" and came up with The $500 Dollar Mythbox Project. The writer there shows screenshots from his Newegg order for the complete system. I used his system as a max price list for each component and started looking around Newegg myself. Here's what I came up with:

Once everything arrives I'll try to document how the project goes in the hopes of helping someone else out there convert to open source personal video recording. Stay tuned!