This started last week as I was about to install iTunes 10.5.1 I was refreshing my podcasts on my MacMini before installing the 10.5.1 iTunes update. My iTunes content is kept on an external drive.
In the middle of downloading podcasts I got the spinning beachball and the bars in the status window stopped moving. I force quit and went ahead with the update. I reopened iTunes and without prompting it returned to the download of the podcast, the bars were not moving and the beachball returned. I deleted the podcast from the iTunes folder, reopened iTunes and still got the beachball and the frozen download screen. I tried installing the update a couple more times and gave up.
A couple days later I looked up how to delete iTunes from my Mac and followed the instructions here: http://www.iclarified.com/entry/index.php?enid=4045. I did this in the admin account and reinstalled iTunes. I opened iTunes in the admin account and it worked but when I logged into my account it remained frozen still trying to download the same podcast.
I then repeated the delete process for iTunes in my account and reinstalled iTunes. When I opened it again it was still frozen and trying to load the same podcast.