Here's an authentic one that I found on ebay. You can see the difference (instead of me trying to explain it).
LOUIS VUITTON MONOGRAM AMBRE CABAS PM HANDBAG TOTE - eBay (item 300236574098 end time Jul-01-08 22:06:39 PDT)
pbeane1 - I'm really sorry that your bag is fake. Is there any way to get this sweet old lady to give you your money back?