In Windows, go to Control Panel \ Clock, Language, and Region \ Change keyboards or other input methods

There you can add a French AZERTY keyboard.

To switch between the 2 keyboards, you can press:

Alt + Shift (on Windows 7)

Win + Space (on Windows 8)

Now, you need to learn where are the French special characters on that AZERTY keyboard. One way to do it is to stick little pieces of paper with the French character written on it on your actual keyboard.

This is not the easiest way to type French characters, but if you manage to learn that, you will know how to type on a French keyboard like a French person does, and without even owning that keyboard :)

French people in France use the azerty keyboard, but it's not very practical for users of qwerty keyboard.
A good option is to choose in Windows the Canadian keyboard called "Canadien multilingue standard" (Canadian Multilingual Standard keyboard) which feature a qwerty keyboard with the é, è, à, ç letters next to the "enter" key.

http://fr.wikipedia.org/wiki/Association_canadienne_de_normalisation

I had same problem.   If your keyboard is "english"  it is a "Qwerty" keyboard.  French keyboard is called "Azerty".   You can change the keyboard format on any Windows OS, just go into "control panel" and select keyboard options so you can change the language.
I also recommend getting small "azerty" keyboard stickers to put on the keys of your Qwerty keyboard (try ebay).  That way you know which keys to press.

If this is too complex and you are not computer-savy, simple use the alt-codes (use the number keys on the right side of you keyboard, not the ones above)    For example, pressing alt + 130 creates " é "    alt+131 creates "â"  so-on and so-on.   Just look on the internet for alt codes and foreign languages.
One problem:  These codes don't work when chatting on skype.

Chez moi c'est le 4, donc vous devriez continuer a' chercher et signaler les accents, etc.. quelque part sinon on s'y perd.

l'accent se trouve sur le bouton : le chiffre 2