Download and burn a business card or netinst image of squeeze or wheezy. I chose wheezy as my target was Sid/Unstable and it currently lags by only 2 weeks. During the install I had to revise the sid plan as the files were inconsistent (you can choose your distro from the installer) and install wheezy. After installing if you want to, which you probably do if its a desktop system, you can change the sources.list to sid/unstable from wheezy and be happy. No need to upgrade anything, wheezy is current enough and future installs will be the latest at all times.
- Install rEFIt from macos (easy, just get dmg, double click package, enter password)
- reboot twice second time should have refit menu (something to do with apple's firmware) If not, see refit trouble shooting section
- In spotlight type "disk u" and choose the first option.
- Live resize your mac os partition to make free space for install
- insert install cd while booted and restart (wont be recognised by refit if inserted while restarting, physical mechanism is too slow)
- Select penguin with disk symbol and boot install CD, install
- Use guided and setup your partitions (gpt, root, swap at the least)
- Install grub in /dev/sda (I did this later, but should work in the install too)
- Eject disk
- Reboot
- Penguin should now have hdd symbol, choose, enter grub
- press e before the time out and remove quiet and add acpi=ht
- Watch debian boot and be fast etc.
Fred.