I´ve updated the 6720s boot CD. Basically is the same boot disc for 10.6 retail disc but it holds a new drivers installer to support 10.6.5 and the lastest 10.6.6. It has many new features and includes lastest (and best) DSDT by juanerson. Download the full package from the HP 6720s section and follow the readme.
HP 6720s downloads
XxX Install Disc