(Assuming you are on Windows)
The source is available on GitHub. To get there, go to http://powdertoy.co.uk and where the other platforms button is for download, choose to view source on GitHub. On the GitHub page, choose the download zip button. Then search the wiki for Required Libraries, and extract that to the folder called powder-toy-master and run generator.py. The, set up a visual studio project using the guidlines on the Building for Windows page. When you are done, try compiling. If it works, move on to coding elements or source files. If there are errors, report them here. I will be glad to help you if you need anything else.
Github got DOSed? AAAHHH-HA-HA! Serves it right! It was probably.....US!
Use mniip's links and then continue on using the building for linux tutorial. Good luck