Eclipse executable launcher error: Unable to locate companion shared library now includes my answer for when Cygwin's unzip utility fails (hint: use another unzip program).
April 2012 Archives
If you try running Cygwin from another program (say, the Ponderosa tabbed terminal emulator) and you get a "missing cygwin1.dll" error, you should check that you have put Cygwin into your Windows PATH environment variable. Cygwin does not do this by default.
(Documented in the Cygwin manual "Chapter 2. Setting Up Cygwin", section "Environment Variables" (but missed by me on the first pass).)