The French conditional perfect (also called the past conditional) is used just like the English conditional perfect. It is used to express actions that would have occurred in the past if circumstances had been different.
The conditional perfect is often used in si clauses with the unmet condition in the pluperfect:
Si je l'avais vu, je l'aurais acheté.
If I had seen it, I would have bought it.
Il serait venu si nous l'avions invité.
He would have come if we had invited him.
The conditional perfect can also be used in a sentence where the unmet condition is only implied:
À ta place, je l'aurais dit.
In your place, I would have said it.
Elles auraient dû acheter un plan.
They should have bought a map.
Use the conditional perfect to express an unrealized desire in the past:
J'aurais aimé te voir, mais j'ai dû travailler.
I would have liked to see you, but I had to work.
Nous aurions voulu manger, mais c'était trop tard.
We would have liked to eat, but it was too late.
The conditional perfect can also report an uncertain / unverified fact, especially in the news:
Il y aurait eu un accident dans le métro.
An accident in the subway has been reported.
Six Parisiens seraient morts.
Apparently, six Parisians have been killed.
http://french.about.com/library/weekly/aa040800.htm
French is my second-language
