Here are the factory instructions. Note that you do not really have to remove the passenger seat. You can just move it all the way back, so that you have easier access to the plug under the seat that the wire needs to go into.
Your kit should have included (2) longer seat bolts than the ones currently holding your seat down in the front rail. This is to accomodate the extra height of the deactivation bar once installed. After installing the bar, you will also need a Porsche PST2 or PIWIS computer (ie. a Dealer visit), to have them activate the bar, so that the car will recognize that the bar has been installed. Once that is done, when you plug the seat belt from the baby seat into the deactivation bar, your airbag light on your dash panel will flash for about a minute when you start the car to let you know that the airbag has been deactivated in your passenger seat side.
Airbag deactivation bar installation instructions:
http://www.whiteson.org/boxster/tsb/tsb.6923.deactivationbar.pdf
Pic of mine installed:
