I installed on my Vista 64bit machine as an administrator via Impulse and was having an awful time getting the DLC. I redeemed my codes on the Bioware page and was logging in on the main screen of the game just fine. I could even start up my EA Download Manager and see that I had three content items waiting to download. But, when I tried to look for DLC in the game, nothing came back. At all. Not the content I should have been able to download and not the content Bioware still wanted to sell me.
But I found the answer over in this Bioware topic. It turned out the program designed to handle all the downloading had not installed, for whatever reason.
If you want to check this real quick, open your Control Panel, select the Admin options, and double click on the Services. There should be a service on the list called "Dragon Age: Origins Updater". If it isn't there, that's your problem. Follow the instructions in the post linked above to get it installed. You may have to start the service up, too.