To be honest I wouldn't bother with the laptop. Without the expensive adapter, VGA isn't an option, and S-Video is going to look like total crap on a large LCD. Plus you'll have no TV tuner unless you go with an external USB tuner, something I don't recommend.
Specific mobo's, cpus, ram, etc. are a dime a dozen and subject to personal preferences, budgets, and agendas, so I won't try to recommend a specific brand or model. Primarily because an HTPC doesn't need anything specific there, as they tend to be fairly low-horsepower machines if you use proper components. The most important thing with mobo's and cases are formfactor.
The critical components in an HTPC as opposed to a regular desktop are
1. Video output. MSI makes a 7300GS card with HDMI/HDCP 1080p output that also routes the soundcard's S/PDIF audio over the HDMI connection. It's like $75 via PriceGrabber[=http//computers.pricegrabber.com/video-cards/m/30725135/]$75 via PriceGrabber
. I don't have personal experience with the card nor have I read a review, but I like MSI's stuff and the specs certainly look adequate. It's also a fanless heatsink design for reduced noise. It would suck for modern gaming, but you aren't looking for that. Personally I have a 6200 card with component and DVI out that I bought a couple years ago, that suits me fine. Then again I don't really use my HTPC anymore for TV watching, so I've not been anxious to upgrade it.
2. Tuner/capture cards. Unless you're only interested in watching DVD's and ripped videos, you'll need at lease one tuner/capture card. The defacto standard for HTPC's is Happauge's line of WinPVR cards with built-in MPEG encoders, usually the 150, 250, and 500 models. The 500 is a dual-tuner model which is essentially dual 150's in a single card. Having hardware encoding takes a huge load off the PC, keeping your horsepower requirements (and therefore cost, heat, and noise) lower.
3. Size. HTPC formfactor is something to be considered. The smaller the better, usually meaning a microATX or miniITX mobo and case. Which means your components needs to be chosen wisely because your expansion options will be limited. There are actually miniITX mobos made specifically for HTPC's that contain onboard MPEG encoders and such. Personally, I prefer a regular desktop mid-tower case for a PC. I bought something attractive that fits nicely within my home theater setup, in the corner beside the massive H/K subwoofer (the case and sub are almost the same bronze color). The wife accepts it, so all is well. ) That gives me more flexibility in choosing components, and also lets me use larger fans that run quiet.
4. Heat. Due to the typical small case sizes, often stashed in a rack or entertainment center, temp control is a problem that must be dealt with. Lots of airflow is needed, both within and outside the case. Fans help, but small formfactor cases tend to employ small, high-RPM fans that lead to the next problem...
5. Noise. The cooling requirements of small formfactor systems tend to be dealt with by an abundance of fans, which introduces noise. While fan noise in a desktop PC or laptop might be tolerable, it's annoying to have a loud HTPC rig when you're kicked back and enjoying a movie. And especially in the bedroom, where it's running while you sleep (assuming you're using it as a PVR). The PSU you choose can also contribute to the noise level if you don't choose carefully.