Per this Flyertalk thread, the deal appears to only work for November 23-27, 2009. A great rate, presumably intended as 520 euros.
Go to starwoodhotels.com and search for Paris, France. This hotel should appear as ‘from 52 euros’ .. Click through and if the rate doesn’t come right up, sort from low to high.
The only thing that gets in the way for some folks is if they have a SET CODE in their profile (if you don’t know what one is you probably don’t). If the rate doesn’t come out, log out and try again.
It’s an internet-only, prepaid rate. The rules permit you to cancel for a single night’s penalty of 52 euros. In practice they may not charge your card right away, I’m guessing they’ll be happy to let you cancel without penalty (but this isn’t guaranteed), and they may not honor the rate — wait a couple weeks before booking flights to Paris — but as a prepaid rate there’s a good chance it’ll be honored.