The only way to download the gnurpgm suite is to use git for downloading it due to it's current developement state.
Once things are better I'm going to provide precompiled packages which you'll just double click'n'go.
First, you'll have to install the official Qt-SDK from here: http://qt.nokia.com/downloads/sdk-windows-cpp-offline
(Attention: This download is approx. 1.8 Gigabyte big and will take some time!)
Next, you'll have to install any git client.
For the following instructions we'll use the vanilla git client.
You can download it from here: http://git-scm.com/download/win
Where you actually install the git binaries doesnt matter ("C:\Programm Files (x86)\Git" is just fine).
During the Installation you'll be prompted to select a option that makes git available for the Windows Command Prompt as shown below.
The rest of the setup contains mainly "Clicking Next" tasks. Go for it hero.
The following steps are numbered on the image below to provide you some visual feedback of "waht da hack am i doing here?".
Let's download gnurpgm using git!
Open the gnurpgm.pro file with QtCreator and hit the bottom-left play button.
Depending on your processor the build process might take some minutes and gnurpm will be started afterwards.
You can view the recent changes here
On Ubuntu, Debian and all it's deriavtes you can press ALT + F2 to open a command prompt.
Open up a terminal over there by typing "terminal". Any suggestions should appear, like "konsole", "xterm" "gnome-terminal".
Whatever suggestion appears, hit enter.
Once you've opened a terminal copy the following into it (to paste the text hit CTRL + SHIFT + V)
Proberbly apt-get stops some times to ask you [yes/no] questions.
Now let's download gnurpgm! Paste this in a terminal and the download starts.
Next time you open your personal folder you will see that it contains a folder named "gnurpgm" now.
Open the gnurpgm.pro file with QtCreator and hit the bottom-left play button.
Depending on your processor the build process might take some minutes and gnurpm will be started afterwards.
You can view the recent changes here