I could not get Chameleon to launch OSX so I decided to use grub to launch OSX. Ubuntu 9.10 has moved to Grub 2, different from legacy grub. Ubuntu will detect OSX HFS+ boot partitions and create boot menu items and scripts but I it kept on getting kernel panics when I used the grub boot menu ... something to do with invalid number of arguments somewhere in the stack.

Also, unlike legacy grub, grub 2 can read HFS+ partitions.

In Ubuntu, use Gparted to find out which partition has your OSX installed.

Then add a very simple menuitem in Ubuntu grub configuration file:
/boot/grub/grub.cfg (note: used to be /boot/grub/menu.lst in legacy grub)
Use any editor. Make sure you have to have admin privileges to save the changes.

menuitem "Mac OSX boot or whatever you want to call it" {
insmod hfsplus # loads hfs+ module. Grub 2 can read hfs+ files !
set root=(hd0,6) # your partition may be different
multiboot /boot # used to be called kernel in legacy grub.
boot # not really necessary; it is implied
}

Now reboot. You will see your new entry in the grub boot list. Use arrows to select it. It will now boot into chameleon.

I think someone can make it better.