In some cases the framework is included with the installation disk that comes with Windows. Just plug in the disk or mount the image using a Virtual Image mounter of your choice. Navigate the disk and check whether it has a folder named sxs. This can be found under the D:\sources directory where D: is the driver letter assigned to your disk or image. If the folder exists the framework can be installed using the following steps.
Press the Windows Key to show the Metro interface.
Type “cmd” without the quotes and right click on the command prompt icon and select run as Administrator.
Type the command: DISM.exe /Online /Enable-Feature /FeatureName:NetFx3 /All /Source:D:\sources\sxs /Limitaccess into the command prompt where D: is your disk drive or virtual drive image letter.
Oflline installation without the disk.
If you are like me and do not have the a disk or the image or if for some reason your disk does not have the sxs folder on it you can download a zipped version for the 64 bit version here or if you use a 32 bit version you can download a copy here.
Extract the folder into your root drive.
Open the command prompt as Administrator and enter the command: DISM.exe /Online /Enable-Feature /FeatureName:NetFx3 /All /Source:C:\sxs /Limitaccess where source is the path to where you extracted the folder.
NB Downloading the full service pack installer from Microsoft does not work. Attempting to use this installer will get you the prompt to download the framework from the internet even if you have downloaded the full installer.