AppleTV is not accessing the iTunes Store after updating software to version 5.2
I was able to accomplish a restore by plugging the AppleTV into my computer with a Micro USB cable, and using iTunes to restore it. 

(I kept digging and found this article: http://support.apple.com/kb/HT4367)

After doing the restore, re-connecting to my Wi-Fi network, and putting in our iTunes account info, the rental showed up immediately, and we can browse the store content again!

Still haven't had time to watch it the movie, though...

Edit: We were able to successfully watch the movie last night.