monitor and keyboard in other rooms, same computer

For a 50-ft run you have two options:

(1)   Use a network cable (much easier to run the separate cables for video, sound, keyboard & mouse)  and buy one of these:  
http://www.amazon.com/StarTech-com-IPUSB2VGA-Ethernet-over-Converter/dp/B004C3Y07U/ref=sr_1_1?ie=UTF8&qid=1346510051&sr=8-1&keywords=ipusb2vga

(2)    Assuming your video card supports dual displays, you could simply run a long video cable;  and use a USB keyboard/mouse with an active USB extension.

The only issue is the cable lengths.    

For the video, if you use a VGA connection for the 2nd display, you can easily run cables up to 100 ft.    If a  50' run is all you need, this would work fine:  http://www.monoprice.com/products/product.asp?c_id=102&cp_id=10201&cs_id=1020103&p_id=3619&seq=1&format=2

DVI cables have more stringent length restrictions, but can still be used up to 50'.    However, DVI cables of that length are notably more expensive then VGA ones.   e.g. here's a 50' cable:  http://www.monoprice.com/products/product.asp?c_id=102&cp_id=10209&cs_id=1020901&p_id=2185&seq=1&format=2

For USB runs, there are more significant length restrictions;  but if you use a active cable (with a repeater), you can still run 49 ft.    http://www.monoprice.com/products/product.asp?c_id=103&cp_id=10303&cs_id=1030301&p_id=7643&seq=1&format=2

Then you just use a USB "desktop" keyboard/mouse with the receiver connected to the USB cable [or you could use a hub if you have other devices you want to connect (e.g. a USB flash drive)].

I really like the idea #1.  That device seems like using Ethernet and USB, it takes care of both the remote video disply and the keyboard/mouse issue. It also sounds like that would work for getting HD from my computer to my TV, so maybe now can get Netflicks going, as well?  But, that is another subject.  The main thing is I want to use my office computer for stuff I do in my music room, so I think that will allow me to keep the computer in my office, but see the display and use the keyboard in  my music room, right?   Along that idea, I have  a Firewire box/device..a Presonus Firebox. It allows me to plug my guitar into a port and the analog signal gets converted to digital and goes into my Cubase for recording music.  That Firewire device, how could get run the cable back to the computer up to 50 ft away?  The Firewire device would need to stay in the music room, as it has knobs for sensitivty that need to be adjusted while playing the guitar