Laufender Computer aus einem separaten Raum

If I get a new video card and monitor that supports HDMI, would I be able to run both audio and video through it?

yes

Would the monitor have to have an audio out?

Only if you wanted to use something other than your monitor for the audio (and even then, there may be other ways).

could I send two monitors on 1 cable or would I have to use 2 cables?

No idea, but guess only one monitor per cable.

How about sending mouse/keyboard through the HDMI cable?

That's not possible.

Not sure if it would allow me to run graphics acceleration and watch movies, does anyone know more details about what this would allow me to do?

You can do this, but it seems inefficient to use two computers in this way, and I don't think you'll get the same performance as you would with just the one computer used directly.

My two cents is to use as few digital cables as possible. So that's ideally one HDMI and one USB. Alternatively you could use DVI, digital audio, and USB.

Never tried any of this though:)

Edit:

Can some be wireless or other methods?

Great idea! Yeah, there are both proprietary and standard solutions I believe for doing this with audio and video. I'd recommend avoiding devices that take analogue inputs (even though they'll no doubt convert to digital before transmission). One site that popped up in Google was this one: http://www.wirelesshdmi.net/. The keywords currently seem to be WirelessHD, WHDI, and WiGig.

I was originally thinking you could do something with DLNA, but I'm not so sure. (I think it's more movie playing than just streaming a constant live signal.) Does anyone know for sure?

Edit 2:

One consideration with wireless though is that it will add extra latency to the signal, which will manifest itself as a slight lag between giving input, and seeing the result on screen. I have no idea if it would be negligible, small, or awful (and it will be affected by the strength of connection between the two transceivers).

DisplayPort claims to support multiple video streams (daisy-chaining multiple monitors), audio streams, and aux data like USB 2.0 and ethernet.

I've never used it, and I have no idea if many/any manufacturers support all that yet, but on paper it sounds like a great solution.

Edit: It would appear you can get both HDMI and USB extenders that operate over Cat5e/Cat6 network cable, so this might be your best option. For example products: HDMI, USB. The USB extenders my search brought up all only state USB1.1 support - this would be too slow for attaching external drives (aside from small flash drives, perhaps) but fine for your keyboard, mouse and other similar controllers. That should cover everything (display and sound via HDMI, control via USB) and not as expensively as I thought the extenders might be. I suggest you look for reviews before buying such devices though, in case they introduce an amount of latency which may be unacceptable for your use of the machine.

Previous answer with a more negative view on cable length limitations:

The main problem you are going to have is cable length limitations. What sort of distance are you expecting the cables to need to run?

I don't know what the longest length the DVI standard officially supports, but the longest extension cable I've seen is about 4.5 meters. HDMI is likely to be similar.

Assuming your keyboard and mouse (and other controllers if you have them) are USB based then there is a limit of 5 meters between each device, so you would need a hub at least every 5 meters. You can get 5m "active" USB extension cables which are essentially single port hubs with a long cable, so you could chain these together to remove the need for hubs. In either case you will be introducing latency with each step (the 5m limit on USB cables is due to signal timing issues, not electrical power loss over the distance) though probably not as much as you would notice.

The other main option is remote control via software like Remote Desktop (windows), NX or just plain X (Linux and similar), or other such solutions. This would mean still needing a full PC upstairs, but you could grab a small low-power low-noise Atom-based machine for upstairs and use it to remotely control the fat noisy monster in the basement. This way you only need an ethernet cable running around the house which can be up to 100m long removing the cable length issue. You could also use a KVM-over-IP unit to achieve the same effect in an OS agnostic manner (you would even be able to interact with the machine's BIOS). Remote control (including via KVMoIP) has one major drawback though - you will not be able to run highly graphical tasks well, if at all, which includes videos and games.

you could use something like Gotomypc.com if you have a second computer like a laptop or a iproduct to control it