This hint will let you create a new disk partition without destroying your data, or actually partitioning. What do I mean? I think this warrants some explanation: Instead of partitioning your hard disk to divide the space between two different volumes, you will make a disk image that is invisible. This disk image will be automatically mounted when the system boots, and it will look and feel exactly like a hard disk partition. The only difference that should be noticeable is that you cannot boot from it.
Hopefully most of you will find this one easy. It does require a little Terminal usage, but I'll step you through it.
[robg adds: I haven't tested this tip. If you do so, be careful with it, especially if you choose to later remove it -- any files not backed up from the 'partitions' will be lost when you delete them. I don't think this will work as described in Tiger, due to changes in handling diskmounting, but I'm not positive.]
Installation
sudo mv ~/Desktop/Partition.dmg /.Partition1.dmg
This moves the partition file you created off your desktop and makes it a hidden file. If you wish to make additional partitions, use Partition2.dmg then Partition3.dmg and so on.sudo mkdir /Library/Hooks; sudo echo "#! /bin/bash" > /Library/Hooks/MountFakePartition
This will make a script that can be run before login. Skip this step if you have done this at least once already.sudo chmod +x /Library/Hooks/MountFakePartition
This will make the script executable. Skip this step if you have done this at least once already.sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool true
Enable disks to be mounted without user intervention. Skip this step if you have done this at least once already.sudo /usr/bin/defaults write /Library/Preferences/com.apple.loginwindow LoginHook /Library/Hooks/MountFakePartition
Have the script run right before login. Skip this step if you have done this at least once already.sudo echo "hdiutil mount /.Partition1.dmg" >> /Library/Hooks/MountFakePartition
This will add the mounting of the partition to the script. Change /.Partition1.dmg to whatever is necessary if this is not your first time to do this.$ sudo rm -f /.Partition*
$ sudo rm -f /Library/Hooks/MountFakePartion
Enjoy!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050427211626863