The following solution from user rellampec has worked for me:
topic428.htmlcopy and paste it here:
Hello.
I had the same problem as you. But, One solved:
First: I'd installed the last version (0.6.1).
Second: I've privileged access to my computer.
Third: I've WinXP SP3
Then. You must to Open --> Menu/Edit/Preferences...
There you will see: General | Dynamips | Capture | Pemu
It's main important to have correct Path configuration on Dynamips (mainly) and Pemu.
In some Windows No-English-Lenguage Operating System Intallations the ProgramFiles FolderName have another Name (in spanish: "Archivos de Programa"). Then, please check if you have the correct path to "C:\[YouComputer_ProgramFiles_FolderName]\GNS3\Dynamips\dynamips-wxp.exe" for Dynamips, and "C:\[YouComputer_ProgramFiles_Folder]\GNS3\pemuwrapper.exe" for Pemu. Is as easy as clicking the button with [...] (three points) and select the Application Name in its Folder.
Once you've configured the correct paths, you must to click on Apply Button, and is also better to click over Test Button (Dynamips TAB) before close the Preferences Window to be sure that all is correctly configured (the result must show you "dynamips successfully started").
Then you can create another Cloud, and see if there appears any NIO Ethernet option.
NOTE: I think is not needed to create a loopback interface if you real intention is connect your router/pix/switch to a phisical interface, since phisical interfaces appears also between the NIO Ethernet options, and they also work good if you choose them to make connections.