new hard drive and OS, do not want to lose files...

I am currently running an 03 Powerbook G4 (1GHZ/256/40) with OSX 10.3.9. I am going to install new RAM (1GB) and hard drive (160GB), as well as new OS. Hoping someone might have some suggestions on the best way to back up my current hard drive...I will copy existing hard drive to my laCie external using carbon copy or Super Duper, but am nervous that once I save to external drive, replace OS on my computer - will I have an issue getting files back over to my computer from the hard drive if I am not running the old OS? Any suggestions in order to make this easier/foolproof?
Thanks for the help....

You could make a full image of your hard drive using whatever backup program you like, then install the new hard drive and restore the backup to it. This will move your entire installation to the new drive. You can then proceed to install the new OS (Tiger or Leopard?) on top of the old one, preserving all your files and settings. It would be best to do an archive and install, which installs an entirely new system folder, but allows you to keep your user settings and files. This entire process would be very easy using disk utility. Heres a step by step:

1. Plug in external drive.
2. Open Disk Utility (/Applications/Utilities/)
3. Click on your hard drive in the left pane.
4. Click the "New Image" button on the top, choose your external drive as the location to save it to, and choose read/write as the format. Click save. This will take a while.
5. Once done, go ahead and replace the hard drive.
6. Boot from the DVD to install the new OS. Do not install yet, instead open Disk Utility from the menu bar.
7. Click your new drive on the left pane. Go to the partition tab, click options and make sure to format the drive with Apple Partition Map. Go ahead and format it now.
8. Once done, click the restore tab. Click the image button and find the image you just made on your external drive.
9. Click restore and go read a book for a while.
10. Once that is done, you will have an exact copy of your old installation on your new drive. You should exit the installation and reboot to ensure it is working.
11. If all is well, boot from the DVD again and proceed with the installation. When you have the chance, click options and choose "Archive and Install" and be sure to preserve user settings. Let the installer do its thing and you will have the newer version of OS X while keeping all your files and settings.

Remember that if anything goes wrong along the way, you still have a complete backup in the disk image you made, and also on the original hard drive, so don't panic. If you run into any problems, let me know and I will try to help.