I use Mozilla Thunderbird as my RSS Reader and Usenet Reader (I don't like using Outlook for RSS feeds, because in my mind, it clutters things up).
I was using version 1.5.0.9 and periodically it would tell me there was an update and that I needed to restart for the update to take place. At which point, I would click on the 'Restart' button, it would restart, and I'd go on my way.
Except it was never updating. I don't know if or how Vista was causing the issue (seems like a good guess), but the only way I could get the update to install was to download the full installer from Mozilla and run it as administrator.