The most common BookPC is the BookPC i810, which uses the Intel 810 integrated video/sound/etc. chipset. RAM is standard PC100 (PC66 should work, but PC100 is cheap and has a future). There are two RAM slots which take up to 256M each, or 512M total.
The sound is 4 channel AC41 compatible. There is an option for digital / optical sound interface though I've not seen it anywhere. The FSB is BIOS selectable as 66, 75, 83, or 100 MHz which would seem to allow overclocking or even Pentium3 use, but there has been almost no success with anything but standard (Mendocino i.e. pre-Coppermine) Celerons (mine is the 533).
Cost is only $129 bare-bones (the cabinet, motherboard, floppy, and installation CD) at eMailPC in Milpitas, CA. The IR cordless keyboard/mouse is $29; 5 speaker sets for $35 on up, etc. I got the bare-bones unit, 128M of PC100 RAM, and the Celeron 533 for about $400 total, including tax. It replaced my '486/160 **very** well and sits under the in box on my roll-top desk. Expandability is nil (OK, more RAM and the USB), but for Web browsing and Email, it works extremely well with my @Home 2Mbps cable modem and its built-in 100bT Ethernet port.
The TV output quality is poor compared to an SVGA monitor, but then again that's TV. There's a lot you can do to adjust and optimize it (see PCWave.com's site). I've not tried the SVHS connection to my 28" Sony yet.
Its intended market appears to be a set-top box: with a DVD drive it would serve as a DVD player, plus Web browser, Email unit, MP3 player, and so on in a tiny set-top size. Too bad the power supply's cooling fan sounds like a 747 at takeoff.
I like mine a lot. It will serve its role very well until I get my Pentium 4 DDR Ram machine next year. Meanwhile my wife uses it all the time for the Web. And it's cranking out SETI@Home work units every 10 hours. For $400, how can you beat that?
As for using an i-opener's LCD as a display: No can do, folks. The built-in display of an i-opener, laptop, or such gets its data from dedicated chips connected to internal system data busses directly. There's never a stage of SVGA video or such. So the only video signals from *any* PC would be incompatible with any point in LCD equipped machines regardless of their source. Rube Goldberg setups which redigitize the SVGA video and pump it into the PCMCIA or USB connectors may be possible but would be expensive and the display quality would suffer horribly. Too bad, too: eMail PC shows off their BookPCs at local computer shows using the Acer 15" LCD and it's stunning - usually playing a DVD with surround sound. Wish I could afford one of those $795 displays...