Try this...

Adapted Code

1. void setup() {
2.   size(500, 500);
3.   open("rundll32 SHELL32.DLL,ShellExec_RunDLL " + "HxC.exe");
4. }

Or open(sketchPath("HxC.exe"));

Yeh i cant seem to get it to work on Windows 7. Real pain. .Exe opens fine on its own - yet ive tried all the above methods and nothing works. The exe doesn't open. Occasionally i get a java se binary error in windows ?