you don't need special software and accessing accents is dead easy. I work in French most of the time yet use all my software in english with us keyboard (primarily because FCP's localisation is awful with jargon that does not make sense).
With US kbd é (e with accute accent) is accessed by typing alt+e and e again. Accent grave is alt+the key left to your z key (the delete marker key) followed by the letter that has the accent. Circumflex accent is accessed by alt+i and then the character you need. Finally a ç (C cedille) is obtained by hitting alt+c.
This will cover most of your needs. More characters can be spotted by opening the keyboard viewer from macosx.
Hope this helps
oh by the way, alt+q will produce the oe attached that should be used when writing oeil (eye) or oenologue, which reminds me that I have a fine bordeaux bottle to open up ;-)