Well, the point of UAC is to prevent programs from starting. Never had Vista, personally, and only ever had to support a few machines with it, so don't really remember how the UAC levels worked there or if they even existed. 7 - 10 however, you can set the UAC to different levels.
Here's the thing though, if this is a problem related to UAC, and your only option is to live with it or turn it off, you may have to just disable UAC to prevent the annoying startup behavior.
If you never through your action or inaction allow malicious programs to start on your computer, UAC is just an unnecessary nuisance.
Try booting the computer with UAC disabled and see if the problem goes away. You can then decide at that point what you will do with UAC, if the problem is solved.