The last time I attempted a major OS update, the world ended as my computer knew it, resulting in a complete clean reinstall of everything! Needless to say, all emails were lost. Everything else was backed up, thank goodness.

I've finally gotten up the courage to reattempt the update but this time I would like to make sure all my emails are intact on a backup.

If anyone knows how to do this, I would appreciate your expertise.

Using OS X 10.4.6 (currently), with Mozilla Thunderbird for email service. PowerMac G4 (PC, not intel).

Thanks very much!

Use this tutorial http://www.mozilla.org/support/thunderbird/profile.
It gives you all the information you need to back-up and restore the data, you'll probably want to put the files on a CD or Flash drive just incase something happens to your HDD partition.

Thanks very much!

I also found that I could save them as html files, which is fine, except it must be done one at a time, which is laborious, but functional.