If you are using a resolution of 1024*768 or higher, don’t go for those cheap passive boxes with a switch! They can’t handle the bandwidth!! (well at least the one I tried couldn’t) maybe try one if you can return it if it isn’t good enough. I bought one, and two monitor extension cords and the screen was way too blurry! (I have room for only one monitor, for two PC’s)
I made a much better monitor extension cable for free!! ;D I removed the monitor cable from a malfunctioning monitor, and added another D connector to the other end and it worked way better than the bought one!! 8)