how to repair volume

Insert the Install DVD and boot from it by holding down the C key prior to the startup chime. Then, in the menu options you will find lots of goodies like password reset and the much desired Disk Repair. Run that so you can do a Repair Disk instead of just a Verify Disk. If errors are found, as will probably be the case given OnyX's warnings, repeat the Repair Disk activity until no more are found. Should also do a Repair Disk Permissions for good measure, although you only need to do this once.

The reason you need to restart with the DVD's mini-OS is that the hard disk has to be modified to do the repairs. And this can't be done if the Mac is using it as the boot source. Note that booting from an optical disk takes LOTS of time. Be patient.

With the Mac already on, insert the DVD, let it mount and pop up on the desktop. Then do a Restart and press and hold down the C key before the startup chime sounds. That key will tell the firmware bootloader to start the system found on the optical drive instead of the hard drive.

Alternately, hold down the Option key. In this case, you will be rewarded with a list of the boot options, from where you can manually pick the optical drive.

When it finishes loading from the DVD, look in the Utilities menu.

You'll have to get past the splash screen, possibly a language selection screen and end up on the main installer window. Ignore and do not use the install options. What you want is to get to that stage, where the menu bar pops up and gives you all the tools you need.

Sorry for not being completely specific, but the last time I visited my SL install DVD was almost two years ago, so memory is kinda fuzzy nowadays.