@ Lurker - huh?
No no, i'm building a home theater PC.
A home theater PC (HTPC) or media PC is a convergence device that combines the functions of a personal computer and a digital video recorder. It is connected to a television or a television-sized computer display and is often used as a digital photo, music, video player, TV receiver and digital video recorder.
The general goal in a HTPC is usually to combine many or all components of a home theater setup into one box. They can be purchased pre-configured with the required hardware and software needed to add television programming to the PC, or can be cobbled together out of discrete components as is commonly done using Operating Systems like Windows Media Center, MythTV, GB-PVR, SageTV, Famulent, or LinuxMCE.
The system looks just like a DVD Player/Stereo Receiver, except it's a computer. This computer does not leave the TV stand, it stays there permanently, and you use your HDTV as a monitor. You don't need a keyboard or mouse (though you may do what you like), the Operating Systems designed for HTPC's can all be controlled through a handheld remote, just like a TV or DVD or Cable remote. The Operating System's interface is typically very simple, and the text is very large so as to make it easy to read, similar to a DVD Player or Cable/SAT Receiver's interface.
The interface and what you'd see on screen would be something like this:
The computer can be whatever you want it to be, but there are cases designed specifically for HTPC purposes, and they're usually like this:
See how it fits in with the rest of your TV stand and how it mimics a DVD player or Audio receiver?
These HTPC's are often configured to be the all-in-one box, so usually they'll have TV tuners in them (which can be controlled in the OS via remote), and used as DVR's. They usually come with a DVD-ROM or DVD-RW (otherwise installing the OS would be a challenge, wouldn't it :P), and so you can use it as a DVD Player (controlled within the OS, via remote). Microsoft Windows Media Center at the moment has no Blu-Ray support, this was the concern I was talking about.
When I say Vista in the OP, ignore that, just think of it as the whole OS being Media Center.