1. What is a HTPC (i know it is an acronym for home theatre PC), but wanted to know what is needed for a pc to be called a htpc.
i have a factory built DELL XPS420. it has vista home premium with the windows media center, intel quad core processors, 4GB ram, 500gb hard disk, pinnacle tv tuner card, ATI Radeon 2600 graphics card. Does this constitute a HTPC?
No hard definition - any PC that is dedicated for the use of a home-theater is a HTPC. So yes, your PC can be called a HTPC if you put it to that use.
But, if you ask the purists, they will say that a HTPC is one that is designed ground up for the sole purpose of serving as a HT media source. Usually this means a AVR like cabinet with a display panel, ultra quite cooling system, fan-less power supply, high-quality Audio & Video components, TV-Tuners with PVR software etc etc. Anyway, these are are not easily available here in India or are too expensive to justify, so I will take what I can get and will call it my HTPC
My graphics card has 2 dvi outputs, but the manufacturer says that i can output to hdmi video + audio. I have not yet tried it as i could nt get a dvi to hdmi cable, but i thought dvi was hdmi minus audio. please can you enlighten me on this?
Currently I use my Workstation PC for HT also. And I do it with a DVI to HDMI cable and cheap 5.1 surround system that is driven directly by the PC (no receiver in between). So yes, get a DVI to HDMI cable and you will get pure digital input to your TV.
You are right, DVI is essentially HDMI minus the audio, but one difference is that HDMI is HDCP (copyright protection mechanism) aware, while DVI is just a dumb terminal. In some situations, I think DVI is better than HDMI if you can get the audio separately as a pure digital feed through a SPDIF connector.
2. I use the windows media center to watch my movies over dvd. Is there a better movie player?
I would recommend PowerDVD. It is EXCELLENT!!
3. What are the high def formats? and which one is the best (this question is assuming that i have a choice of formats to download and i want the highest PQ/AQ)
Well, HD-DVD is defunct and the near future seems to be with Blue-Ray. So that is the only choice with respect to HD discs.
But, on a PC you can have several formats. My favorite is a H264 (a.k.a x264 and AVC) encoded HD file in a Matroska container (.mkv file). I play it in Media Player Classic (mpc) with CoreAVC for decoding. Of course, I think VLC Player is also equally good.
Other formats are DivxHD, WMV-HD, MPEG-2, MPEG-4 etc. Basically anything that can encode at HD resolutions (720p & 1080p).