If you have Windows installed, and you set up sufficient space for installing the OpenSolaris 2009.06 operating system, the installation should be straightforward. All versions of the OpenSolaris software for the x86 platform use the GNU Grand Unified Bootloader (GRUB). The OpenSolaris software recognizes Windows and ensures that the Windows partitions remain unchanged during an installation. When the OpenSolaris installation completes, and the system reboots, the GRUB menu displays both the Windows and the OpenSolaris boot entries.
If you have either the Linux or Windows operating systems installed on your system, before installing the OpenSolaris operating system, save a copy of the menu.lst file. You will need to manually update the menu.lst file to add the Linux information after the OpenSolaris installation completes. For instructions on that, please check: http://dlc.sun.com/osol/docs/content/2009.06/getstart/linuxgrub.html#linuxgrubtask
The installer cannot be used to multiboot the OpenSolaris operating system. However, the installer can be used to replace the Solaris 10 1/06 and later releases in an existing multiboot Solaris system.
Notes on Extended Partitions: If you have another operating system installed on an extended partition, the existing extended partition is neither changed nor lost during an OpenSolaris installation. Existing extended partitions are not visible during the installation, but the primary fdisk partition in which the extended partition resides is visible. No data in these partitions is lost as a result of the installation. The operating system on an extended partition is not displayed in the GRUB menu.
RAID-Z (Redundant Array of Inexpensive Disks) is similar to RAID-5 but it's a bit better because it checksums on multiple disks, so data security is higher and performance is also better thanks to organizing data in a way that the disks are well harnessed (less going there and back to get data).