The VIN number can be seen from outside, through the front left-side front quarter window
in addition to Vin Numbers, Peugeot use RPO (or DAM) numbers that include the date the car left the factory. This means that a number of cars will have the same RPO number.
It should be on the passenger side (UK) B post sticker - picture is from my 1.6 Sport. Many of these cars were stored for up to 18 months before sale.
RPO = 1055681 - 10556 = a build date of 3/10/2005
The last two numbers - 81 = means the car was built at Poissy.
10081 = production line 1 - car #81 of that day from line 1
KSH = the colour "Cayman Green metallic";
20060315 = model year 2006 - serial number 0315
First registered: 28/3/2007 - 18 months later