"He is a tough man."
Translation:C'est un homme dur.
It's a modified noun, so you use "C'est"
For more info: http://french.about.com/library/weekly/aa032500.htm
Um, no. Either way, the noun is modified.
You use "il est" with an adjective, like "Il est gentil", or with particular nouns that refer to professions, like "Il est medecin". (I believe the French actually think of that usage of the noun as being an adjective).
Otherwise, if it's an ordinary noun with "le, la, les, un, une, des" in front, you must use "C'est".