This is a great art but kinda hard to use. It was pretty easy to find out that the tilesize is 32x32, but harder to find out where it starts, and after a while of trying to get a clean background I gave up, googled QNetWalk, found the game and more images, made a tileset and uploaded it all here:

http://opengameart.org/content/computers-and-network-from-qnetwalk