Question about backing up files and reinstalling OS X

what I would do is this:

1) back up all your documents (MP3's, photos, etc.) to your external HD...you could make an image copy of the iMac HD to do this if you wish

2) do an Archive & Install of the OS on your iMac. This will preserve all your applications, files, and user/network settings. Basically, it will just replace the operating system; your data files won't be touched. I believe you can customize the install to your specifications.

3) after you've done the Archive & Install, and verified that all your documents still remain, wipe/reformat the external HD.

4) make an image copy of the HD on your iMac G5, and save it to your external HD.

if you do it correctly, this will preserve all your documents and settings and give you a backup copy of everything.

note that steps 3 and 4 are optional. If you wanted, you could keep the original iMac image copy on the external HD. That way, if your new install doesn't work out, you could return to your old settings by replacing the new install with the image copy.