The assembly guide is the pepakura screen saver. Download it, and under it properties set the pdo file you wish to view, say the helmet.pdo file. Then you can adjust the speed in which it folds up and assembles the helmet, and the same in reverse. Use this as a key on your assembly.
The one thing that threw me for a loop when I started working onmine was the face shield portion. I left mine with the grey coloring so I would be able to identify the outside versus the inside of the pieces.
Spartan-720, it just depends on how much you want to do to your suit. If you just want a cardboard or paper suit that you can paint and carefully wear, you can probably do that in a month or less (even if your taking your time). But if you want to fiberglass it and everything, my guess is that it will take more time than that.
Spartan-183, the virus warning is just something windows warns you about whenever you download an executable (*.exe) file from an "untrusted" site. Any executable file could potentially contain a virus, or itself be a virus. Windows is only warning you of that fact. But Pepakura straight from their site contains no virus or spyware.
I haven't used the screensaver, but I didn't think I needed it either. Just fold the peaks and valleys like you are supposed to and then tape or glue it by the numbers and it should be pretty easy.