The easiest way to get pd-extended on the raspberry pi (raspbian wheezy)
http://puredata.info/docs/faq/debian

but that installed pd-extended 0.42.5 for me, for a more recent version try

Based on Tedbot's tutorial on building pd-extended for Debian Squeeze.

To install run these commands from the terminal:

$ sudo nano /etc/apt/sources.list

-copy/paste this line to the list(right-click to paste):

deb-src http://archive.raspbian.org/raspbian wheezy main contrib non-free rpi

ctrl+o, Enter (to save). ctrl+x (to exit)

$ sudo apt-get update

$ wget https://puredata.info/downloads/pd-extended-0-43-3-on-raspberry-pi-raspbian-wheezy-armhf/releases/1.0/Pd-0.43.3-extended-20121004.deb

$ sudo dpkg -i Pd-0.43.3-extended-20121004.deb

$ sudo apt-get -f install

it should be installed. For root priorities:

$ sudo chmod 4755 /usr/bin/pd-extended

Updated tutorial on how to build pd-extended 0.43.3 for Raspbian Wheezy
http://www.epicjefferson.com/2012/10/raspberry-pi-pd/