Stop dreaming and come back to reality, now you can make it easily. Try Rasterbator, an excellent program which is really useful for resizing pictures by a particular way.
This application is not designed to make pictures have the required size to fit a certain and small place, but it is designed for printing it with big dimensions without losing quality.
How does it make it? Rasterbator calculates the image size and make it possible to print it in several pages, so yuo can put them together and visualize them as a big picture.
Tidy your room because a magnific poster is going to be placed on the wall.