For installing SharePoint Foundations 2013 SP1 offline you require the prerequisiteinstaller.exe file which can be unpacked from the SharePoint.exe file that you may have already downloaded or you can download from here .
For this posting at the Root of C i Created a Folder called "SPF2013" which i copied all the SharePoint Prerequisite files. Within the "SPF2013" Folder i created a folder called "Core" ( C:\SPF2013\Core )
Open up the Command Prompt, you may need to run as administrator
Change Directory to the location where the sharepoint.exe file is located for this posting i used the following command
Now lets extract the prerequisiteinstaller.exe file by typing in the following command
Once you click on enter and execute the Command after a few seconds you should receive the following popup indicating the files have been extracted.
Now just verify that the files have been extracted