Actually, Vista is better for a HTPC (more powerful audio stack, better dxva, among others).

Actually, I don't agree with you at all, but we are off-topic here. If you want to discuss this, feel free to open a topic in another HA forum.

I built a Vista HTPC recently, and while I agree that 'on paper' Vista is a better platform for HT, the intrinsic DRM (which may also be an issue with XP? I don't know.) cripples my system to an unacceptable degree.

I have spent hours trying to get my system to play factory DVDs I own, Netflix on demand, etc. Video card drivers that prevent the user from capturing pure digital signals seem to be the root cause of my troubles, but nothing I've tried to solve the problem has worked.

I know I'm not alone, because there is a thriving market for software which allows you to circumvent the DRM. I am unhappy that I cannot use Vista's built-in software to consume data which I've already legally paid for. In all other respects, I find Vista to be a productive, well-designed OS.

A HTPC is, in a very simplistic way, a mix of a CD player (audio) and a DVD player (video). So it has to remain fast and simple. That's why its OS has to be fast and simple.

XP is a light OS compared to Vista (just take a look at their respective sizes in a hard disk). Yet XP can be made much lighter with well-known utils like nLite. A "light XP" will have a shorter boot time than any Vista version (which is an essential feature for a HTPC IMO), while preserving all functions that are essential to a HTPC.

XP will work better than Vista in old PCs, with slow processors and not much RAM. Vista needs a fast processor and at least 1.5 GB RAM to run decently (and it's still less reactive than XP when both are installed in the same PC with 1.5 GB RAM - I have experienced that).

XP already has all the needed audio and video software :
- foobar / Winamp / etc. for the audio, with Kernel Streaming / ASIO support,
- MPC / KMP / PowerDVD / etc. for the video,
- ffdshow / Avisynth / Reclock / Powerstrip / CoreAVC / etc. for postprocessing and other video stuff,
- etc.

So I don't see any serious reason for using Vista within a HTPC (obviously I won't take into consideration any aesthetic reason). Heck, I don't see any serious reason for using Vista at all, but that's another story.

The extra DRM is the protected video path which will be used by Bluray titles in the future - to my knowledge, no actual media uses it as of now. On my Vista-based htpc, DVDs just play fine, and the DRM (required for legal DVD playback) is included in XP to begin with. I'm not familiar with Netflix, but for DVDs, maybe you just have an issue with your DVD playback software. I use MPC-HC, works like a charm.

foorious: if your goal is being fast and simple, why don't you use Windows 2k instead of XP? It's even faster and even simpler.

I would second Windows 2000, but here's the one issue: You may have a hard time finding new hardware that has drivers written for it (I mean for sound cards). XP is nice, but I hate having to deal with the Windows Genuine Advantage nonsense. And Vista, is, well, bloated with DRM and non necessary foolishness (at least for what you are trying to do).

Therefore, I guess Windows XP, despite WGA, is your best bet. However, you may be able to get away with Linux (actually I'm using Ubuntu, and it works much better than XP, but that's just my mileage); however there is a more limited set of audio applications (especially in the ripping / converting department). Video in Linux also is a big issue, but it's getting better (and if you have VLC, you are pretty much set for any type of video files you want).

Vista runs fine on a Atom330 and 9400M. Granted it has 4GB RAM mainly for its cache. EVR, DXVA2 and Media Foundation are big wins for a HTPC.