I have a copy of an old folder holding a file that has been hidden on Mac OS 8 or 9 (using resedit, if my memory isn't failing). Is there an easy way to un-hide it in OS X?
If you have Xcode installed you can try the SetFile command. The command below should unhide the hidden file.
SetFile -a v hiddenFilename
If you remember the location you saved the file to you can do the following.
Open the terminal and enter these commands.
(show all hidden files)
defaults write com.apple.finder AppleShowAllFiles -bool true
Make what ever modifications you need to, and when your done enter these.
(re-hide hidden files)
defaults write com.apple.finder AppleShowAllFiles -bool false
(restart Finder again)