This is not just a "you" problem. I spent 2 hours in my local store to try and get this issue resolved. I have the nook color, with the 1.4.1 update and it does the SAME THING. Your discription is perfect.
It does show up in my personal section of apps but the app icon of the wallpapers say install &when you push that again green bar goes again but nothing happens & either it will have just lines in the long oval - where the green bar goes across- or it appears install on the app icon again. That is as far as it goes.
I have repeated this error with Apps and Wallpapers. I also have tried with it charged, With the charger plugged in. The 2 hours in the store? We de registered and re registered the nookcolor and it downloaded 1 (yeup only 1) and then the problem repeated itselt. Its truly frustrating and troublesome to see that one one is replying to this issue. Searching on google shows this is a common problem.
Im starting to wonder if perhaps buying the nook color was even worth it at all. perhaps I should have gone with a different device and just downloaded the nook app.