Latex2e is supposed to be compatible with documents formatted for 2.09, but in practice, small or large problems often occur.
Therefore, the style and sample files you should use depend on whether the document is formatted for 2.09 or 2e, and which version of Latex you are actually running.
You can tell what version of Latex you are running simply by executing it on a file. On most systems, the third line of messages will either read 'LaTeX Version 2.09' or 'LaTeX2e'.
Your document is formatted for 2.09 if it begins with the '\documentstyle' command. It is formatted for 2e if it begins with the '\documentclass' command.