File not visible in Finder
From this tutorial on MacWorld, here is a way to show hidden files in the Finder:

Open a terminal, and enter this command at the Bash prompt:

$ defaults write com.apple.finder AppleShowAllFiles YES


Then restart the Finder with the following command (also from terminal):

$ killall Finder


The next time you open a Finder window, your hidden files should be visible.

To echo what Oliver said, you can also use chflags to alter the "hidden" property on a specific file. (chflags man page)

chflags nohidden hiddenfile.ext