Question : photoshop CS3 16-bit image support problems - and are they addressed in CS5?

Using photoshop CS3,  I can open a 16-bit image, change its histogram/levels/exposure to see it better. I know of 2 ways to go about this, but each has a downfall:

A) make changes to exposure etc. to the file itself. The problem with this method is that even if I save the settings (of exposure etc) before I make any changes, then make the changes, do some pixel editing, the old settings are not re-applied when I load my saved settings. (Not sure why). So using this method, I cannot recover the original settings....

B) The second way to go about this would be to make an exposure "layer" mask, do some edits, then it off when saving to save the original settings, but with the edits. However, it seems that 16-bit image layer effects are not supported in CS3. I do know of some plug-ins that deal with this, but would rather not spend $ on a solution.

I have two specific questions:
1) is there a way I can reload the original exposure etc settings in CS3 that I am not aware of?
2) Does CS5 support 16-bit layer mask effects (which CS3 does not).

Answer : photoshop CS3 16-bit image support problems - and are they addressed in CS5?

It sounds like you've made a 'destructive' edit. Image changes can be reset if your image is camera raw. If it's psd or jpg then you're done, that won't be fixed by CS5 or CS10;
AFAIK, CS5 does not improve the editing functionality of 16-bit images. 16-bit images have always had limitations, and still do. That said, you should take 3 bracketed exposures and combine that into a HDR 32-bit image, which eventually gets knocked down to 8 bits for printing or advanced editing.
HTH