To be able to create or modify PE 2.x or 3.x images, install Bootable Media Builder on a machine where Windows Automated Installation Kit (AIK) is installed. If you do not have a machine with AIK, prepare it as follows.
To prepare a machine with AIK
Automated Installation Kit (AIK) for Windows Vista (PE 2.0):
Automated Installation Kit (AIK) for Windows Vista SP1 and Windows Server 2008 (PE 2.1):
Automated Installation Kit (AIK) for Windows 7 (PE 3.0):
Automated Installation Kit (AIK) Supplement for Windows 7 SP1 (PE 3.1):
http://www.microsoft.com/download/en/details.aspx?id=5188
You can find system requirements for installation by following the above links.
It is recommended that you familiarize yourself with the help documentation supplied with Windows AIK. To access the documentation, select Microsoft Windows AIK -> Documentation from the start menu.