Missing 6GB of disk space

Hello, I’m new to working with a Mac, so hopefully this question makes sense. I have a Mac that shows the drive being out of disk space. It shows 9.4GB total space, and 40MB free. However, when I checked the sizes on all of the directories on the drive, they only added up to about 3GB. Being a PC guy (don’t say it!), I feel that the drive must be partitioned, but I can’t find anything to back that idea up.

I tried the Drive Setup on the boot disk, but it wants me to boot from the cd. When Itried that by holding down “c” at startup it ejects the cd and continues booting from the hard drive. Of course, drive setup then tells me to boot from the cd again. Any help would be appreciated.

Thanks