It would appear that Boot Camp is indicating that your HD already has more than one partition.
You would see this in the left hand pane of Disk Utility. Your one hard drive would appear as two drives. You will also see this on the desktop. Both the partitions would appear on the desktop, starting from the top right and going down the screen.
By default, the MacBook comes with the hard drive formatted as one partition, Mac OS Extended (Journaled) (Don't worry too much about the titles.) and as such only has one HD on the desktop.
Somewhere along the line, you, or a friend the "knows all about Mac's" may have partitioned your hard drive into two partitions.
This is unacceptable to Boot Camp which, as you now know, requires your drive to be "as one" before it can go about its own thing. Boot Camp will partition your HD into two sections and will preserve your data in the process.
WIth two partitions, there is no easy way for you to consolidate the two "apparent" partitions into one without lossing ALL your data.
This is the reason for the warning that you should backup all the documents and data that you have created, Quicken Files, iTunes, iMovie, iPhoto etc, and save them to another drive or to a CD/DVD. Depending on the size of your collection, this could amount to a number of CD/DVD's
Once you have done that, you have to FORMAT your drive, using the Restore disks and Disk Utility, into a single Mac OS Extended (Journaled) volume.
When that is done, you can then restore Mac OS X 10.4.x and replace all of your saved data.
Then you are ready to run the Boot Camp installer again.
Any clearer?
P
I'm trying to get Windows XP on my MacBook and I have gotten a little bit stuck in the process. In Boot Camp I get to the part where you create the partition and I always get a message that says, "Your disk cannot be partitioned because some of the files cannot be moved. Back up the disk and use Disk Utility to format the disk as a single Mac OS Extended (Journaled) volume. Restore your information to the disk and try using Boot Camp Assistant again."
I got into the Disk Utility thing and wandered around until I found a place to make sure I had the "Mac OS Extended (Journaled)" thing selected, but the rest of that (about backing up the disk and restoring the information to the disk) is just gibberish to me. Any help would be greatly appreciated!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic