OK, a beginner here

[Reed]

I am just trying to get some things straight.

I have LR 3 and am using the the trial of Elements 9. From what I understand, LR and ACR are non-destructive but PE is not. Does this mean that if I save a file in PE, I can not go back to the original?

This is so confusing.

[RecurrentNerve]

Depends how you do it, Reed. If you use Adjustment Layers for all your changes, don't flatten the image at any point, and save as a PSD (Photoshop) file, you'll be fine. The simplest thing to do is just save a copy rather than saving over the original. Any 'destruction' will only take effect if you save.