Well, alright.
Get yourself an external firewire drive and copy your data files to it.
First you will have to partition the drive using the Disk utility.
Alternative is to image the hard drive to the external drive using Carbon
Copy Cloner. However, imaging your current hard drive necessitates that you
cannot be running the OS from it.
Solution: Use the OS X disk to start your current computer but install OS
X on the new firewire drive that you have connected to it. Once done you can
then start the computer holding the N key down (network) and choose the
firewire drive to start. If that doesn't work then try holding the Option
key down. That will give you the choice of bootable disks to start.
Making an image is one of the cleanest ways to do this because it
restores everything the way it was, but then you may not want it that way so
simply copying the data files that you want saved may be your best option.
Once the image is made you can restore it with the same disk utility or use
Net Restore.