From Genunix

This page gives instructions on how to configure a system to dual boot OpenSolaris and other operating systems. Feel free to add and update entries. Please make it as step-by-step as possible. Here's a wiki on setting up OpenSolaris on a Mac with VirtualBox.
Backup your data prior to attempting any of these procedures (ie. use at your own risk)

OpenSolaris with MacOS on MacBook Pro

Reference: Paul Mitchell's Blog
(This is high level, please add more detail for each step if you can)
(The following was done on a 2.4 GHz Intel Core 2 Duo MacBook Pro with 4GB of DDR2 SDRAM)

0. Setup

 Get rEFIt on a CD or USB stick.
 Get gparted livecd on a CD.
 Have USB mouse available when you use gparted and OpenSolaris.

1. Backup User Data - we are going to start at bare metal
2. Insert Mac OS X (10.5+) Install Disc 1 and reboot
3. Select language after install starts
4. Select Disk Utility from upper left menu
5. Partition Disk

 Example (Note. FAT partition > 32GB):
 Partition 1 - OPENSOLARIS 55GB  MS-DOS FAT
 Partition 2 - MacOS       95GB  Mac OS Extended Journaled

6. Resume MacOS Install (takes about an hour)
7. Boot to MacOS and answer questions as needed.
8. Install rEFIt application and run the following command:

 # /efi/refit/enable-always.sh

9. Insert gparted CD and reboot to CD using rEFIt menu
10. Insert USB mouse
11. Select second GRUB entry (so you can eject CD) and answer keyboard and language questions
12. Open terminal window by double clicking monitor at top
13. Change the 200MB partition 1 type using fdisk:

 # fdisk /dev/sda
 ...
 Command (m for help): t
 Partition number (1-4): 1
 Hex code (type L to list codes): af
 Changed system type of partition 1 to af (Unknown)  

 Command (m for help): w
 The partition table has been altered!
 calling ioctl() to re-read partition table.
 syncing disks.

14. Change OpenSolaris partition from fat32 to linux-swap using gparted application
15. Return to the terminal window and enter:

 # eject
 # reboot

16. Remove gparted CD and replace with OpenSolaris CD/DVD and reboot

 OpenSolaris 2008.05

17. Do the install and at the first opportunity exit the install
18. In the terminal implement the workaround for CR6413235:

 # mount -o remount,rw /
 # mv /sbin/fdisk /sbin/fdisk.real
 # cat > /sbin/fdisk
 #!/bin/sh
 echo "$*" | grep -- "-F" > /dev/null
 if [ $? = 1 ] ; then
 /sbin/fdisk.real $*
 fi
 CTRL-D
 # chmod +x /sbin/fdisk

19. Continue with default install (takes about an hour)

 # install-solaris

20. Reboot Mac OS
21. Update the Linux icon to OpenSolaris icon

 # Use "Save Link As" to save these icons to a temporary folder: boot_linux.png os_linux.png
 # Save the old icons and copy over the new ones (Note. The .png file extension is used to get past the website file extension checker).
 % pwd
 /efi/refit/icons
 % mv boot_linux.icns boot_linux.old
 % mv os_linux.icns os_linux.old
 % cp ~/Documents/boot_linux.png boot_linux.icns
 % cp ~/Documents/os_linux.png os_linux.icns
 % ls
 boot_linux.icns		os_freedos.icns		os_win.icns
 boot_linux.old			os_hwtest.icns		tool_part.icns
 boot_win.icns			os_legacy.icns		tool_rescue.icns
 func_about.icns		os_linux.icns		tool_shell.icns
 func_reset.icns		os_linux.old		vol_external.icns
 func_shutdown.icns		os_mac.icns		vol_internal.icns
 os_ecomstation.icns		os_openbsd.icns		vol_optical.icns
 os_freebsd.icns		os_unknown.icns

22. Here's what you get after you are done

OpenSolaris MacBook Pro Networking

Network setup instructions from Brian Leonard's Blog