You can find a lot of useful informations here: 
However, in short:
- on OSX, install Refit
- boot Puredyne with the live CD/DVD
- partition your HDD with Gparted and add one EXT3/EXT4 partition for your Puredyne system and one for your swap (usually 2 times your RAM size) (note that GUID Partition Table (GPT) seem to not like more than 4 partitions on a drive).
- install Puredyne
- during the install, when you're done with setting up the partitions, don't forget to click on advanced and change where to install GRUB bootloader:
i.e. install it on /dev/sdaX (where X is your "/" puredyne partition) instead of the drive mbr hd0 (which is the default), otherwise you might get in trouble with grub2 and refit.
- finish the installation
- shut down your computer
- start your computer
now you should have a linux icon in your Refit boot menu saying: Boot linux from partition X
- go into Refit Partition tool and synchronize your partitions
- boot into Puredyne
After the installation some things might not work as expected. The support varies a lot from one model to the other. For instance the sound doesn't work out of the box in some imac's , In that case we had to add "option snd_hda_intel model=imac24" in /etc/modprobe.d/alsa-base.conf and restart alsa with "sudo alsa reload" command. Your mileage may vary and is best to consult https://help.ubuntu.com/community/Intel_iMac