At least on the 2009 models, Amazon is only via the TV and not the DVD player.
The widget is through the Yahoo widgets. The 2010 TV models use a different widget scheme.
I purchased an Samsung blu-ray player (BD-C5500) because it had the "Internet@TV" feature, via "downloadable widgets" -- and Internet@TV pages all over the web indicate that Amazon Video-on-Demand is one of the features of this system.
The Amazon Video-on-Demand pages tell you that you can access their service by going to the the Yahoo widget first. But...there is no Yahoo widget available, and no Amazon widget either. What is going on? Is it impossible to access this service, which (along with Netflix) is the main reason I baught this player in the first place!