I've done it in CS, but as I said I don't have it in front of me so I'm not sure how acurate this will be.
Open one of your snaps.
Create a new action (icon to the left of the trashcan) in the
Actions palette and hit record.
Select
File>Save for Web and save the file in a new folder as a 256 color PNG-8 file.
Close the image.
Hit stop on the 'action recording' palettey thing.
Now, in the File menu go to
Automate>Batch...It opens a dialogue asking you for a source folder (your old snaps) and lets you select an action that you've recorded from the drop-down menu. Select the last action you recorded and hit
OK.
It should open all your snaps, then save them as 256 color PNGs in your new folder.
Sorry if these instructions are way off, this is from my fuzzy memory.