This help page explains how to add E-junkie Cart or Buy Now buttons to a Facebook Page:
http://www.e-junkie.com/ej/help.social-networks.htm
Unfortunately, due to the limitations of Facebook, it is not possible to get our overlay-style cart to display "inside" a Facebook page, so any Cart buttons you add there would display the cart as a separate browser window/tab. At present we do not have plans to divert Development resources away from major improvements to E-junkie itself (such as the new Admin project) to investigate whether any more sophisticated FB integration might even be possible.