Engadget has posted a useful step-by-step howto on building your own Tivo-like home theatre PC (HTPC) using MythTV. They list each piece of hardware they used on the way to a successful, smooth install. From the site:

The total for the base system is $988. The addition of the TV tuners brings the grand total to $1126.

This price is probably beatable if you opt for a lower end processor, which will save you some money and really wont cost too much performance-wise provided the tuner cards you choose do hardware encoding. Tuner based encoding takes the vast majority of processing load off of the CPU. That being said, faster is always better when it comes to CPUs, generally speaking, so too severe a drop in clock speed will hamper menu navigation and other features which will detract from the snappy, slick user interface that you want in a PVR. If you're not too Linux savvy and aren't ready to do a manual install, a great way to set up MythTV on a PC is by using KnoppMyth. KnoppMyth is available on a downloadable, bootable CD that aims to make the MythTV installation as straightforward, user-friendly and painless as possible. If your system meets the hardware requirements, the CD will install MythTV onto your system while prompting you for only a minimal amount of configuration questions. If you encounter problems along the way, the KnoppMyth forum is invaluable. The site's admin, Cecil, not only tirelessly develops KnoppMyth, but also personally answers an unbelievable amount of questions on the forum, which, by the way, is packed full of information on getting up and running with MythTV - useful no matter what your method of installation.

Lifehacker has a nice howto on setting up your own personal web server, giving you the ability to do things like stream mp3s from your personal collection to work, set up a web based shared calendar for your family or give yourself quick access to your personal files from anywhere you've got net access. The system is password protected of course, but it is built on a windows box, so beware and be patched.

The iCEBOX Countertop PC "kitchen entertainment" unit offers you Internet connectivity, TV, DVD/CD, radio and home video monitoring to distract you from the maze on the back of the Froot Loops box. The device also boasts a touchscreen and a washable wireless remote and keyboard. If, after installing the iCEBOX, you find there's still not enough technology in your kitchen, you would probably want to go ahead and add the compatible breadmaker sidekick, which comes complete with a database of hundreds of UPC codes preprogrammed in (UPC code updates come from the iCEBOX) linking the scanned item to it's appropriate cooking instructions.