1 computer powering 24 TV screens (50")

Video cards would have to support a lot of outputs. My thought would be an AMD FirePro with 6 outputs or a Matrox card. Matrox would be very expensive and I'm not sure where you'd get it. You would also need a motherb
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.matrox.com/graphics/en/products/graphics_car...

As far as controlling them individually with tablets or wifi. Not sure what you are looking to do here, but it will not be cheap. You are looking for something probably proprietary or special use. Most likely you would have to seek the guidance of a sound and media company that could put together a custom package. My guess it would be tens of thousands of dollars or hundreds to really do that right.

You would have to see if Windows could even run that many displays and the desktop resolution would even be supported in windows. As mentioned it is probably a specialty build with a non windows OS. But who knows. This is not a hobbies questions it is a corporate or large entertainment realm.

thanks jay2tall for the info. Appreciate it. I just looked into the amd firepro and it definitely got me onto the correct track. wish the MST hubs came out because that would make things a lot easier.

There is a new mobo that just came out a few months ago that has 4- 16x PCI-E slots...http://www.anandtech.com/show/6228/asrock-x79-extreme11...

Maybe I could throw in 4- firepro's to achieve 24 monitors. One more question... going from mini DisplayPort to HDMI, distance shouldn't matter right? I can have it travel 40 to 50 feet no problem?

There are a number of workstation motherboards out there that also support (4) PCI-E x16 cards. I do not believe you need it to support Crossfire because you are using them independently. But the Asrock should work, in theory.

Distance of an HDMI cable will matter at some point and you could see some signal loss. However, I think 50' would work. Most cables that length at pretty thick and are $50. You might find you are going to spend a lot on HDMI cables.

May I ask what this is even for?

So, admitting that this is way out of my league, one thought:

Are you by any chance near one of the new Microsoft stores? because this sounds a lot like what they do this in the stores - have TVs on three walls. Maybe you could go ask someone what they use?

By the time you pay for fire pro cards and HDMI cables alone it would probably be cheaper to slap a thin client on the back of each monitor. Really all you need is a device that can send a video signal and be network controlled.

It wouldn't even have to be network controlled I suppose. Something cheap like a rocku, or anything that can do full screen Web browsing, or a TV that can. Point them each to their own webpage being served on your local network, when you want to change content log on to remote desktop or webserver and just change the image that monitors Web page is showing.

More than one way to do it

You might want to look into the junkyard jumbotron. I haven't ever tried to use it, but it might be a better way to link a bunch of monitors together than a crazy custom rig.

http://www.popsci.com/diy/article/2011-03/mit-software-...

Edit: Found a better link.

http://jumbotron.media.mit.edu/

Interesting. Looks like that's to combine displays for one image though. Not drive separate images on each display