By next spring, Apple will have the rest of the Media Center - one of the "super-secret" bits of Leopard is a full clone of Microsoft's Media Center Edition, built upon a greatly enhanced Front Row. (And accompanied by a full-featured AV remote.)
The iTV is just Apple's copy of Microsoft's "Media Center Extender" and/or "Media Center Connect" (see
Media Center Extender or Windows Media Connect. Which Do You Need?) or Intel's wireless extender that will be part of the Viiv platform.
Leopard has the other piece - the real multiple tuner support and PVR system.
Couple that with a dual-core Conroe in a TiVo-sized box, and you'll have the option of a dedicated Apple Media Center in the living room, or the "iTV" feeding from the Apple Media Center in the office.
Windows Media Center Edition supports up to five extenders. Apple certainly will do the same, so whether you choose the Conroe HTPC pizza-box, or a bigger Mac in the office - TVs throughout the house can access the single copy of the media library with "iTV" boxes.