Can't partition hard drive

Just recently bought an iBook from ebay that came with Mac OS X Tiger 10.4.11 preinstalled.

I have a retail DVD of Mac OS X 10.5 Leopard that I want to install on the hard drive replacing Tiger.

However the iBook does not have a "Combo" drive only a CDROM.

So what I did was made a “Mac OS X Install DVD” disk image from the Leopard DVD on another Mac and transfered it to the iBook via file sharing.

The plan is as follows,

Have two partitions, one will be for the installer and the other will be for the Leopard installation.

• With the disc image mounted, open the Disk Utility.
• Click the Restore tab.
• Drag the Disk image file from the list on the left of the Disk Utility window to the “Source” field.
• Then, drag the icon of the partition I want to put the installer on to the “Destination” field.
• Click the “Erase Destination” check box so that it shows a check.
• I also skipped the Checksum.
• Click Restore.

Once the above is complete I should now have a bootable OSX Leopard Install partition?

Now go to System Preferences\Startup Disk and specify the boot partition to be “Mac OS X Install DVD”.

Restart and prepare to install to the other blank partition.

Problem is that when I go to partition the hard drive it will allow me to split in two except

I cannot resize the spaces and the buttons minus the "Options" are grayed out.