Although you can easily fix an ntdll.dll error in Vista - there are many methods
you can try; but this utility is without a doubt the best one out there at the moment. But can we be entirely sure of these utilities for every problem, all the time? That's probably not the case, still, i think that it's the answer you need to tackle your current error problem and others down the line. Believe me (i've been there), if you're starting to get error messages it's a good idea to make sure that your windows is current and you've installed the latest updates. Not long from now - no doubt very soon - most of us will have such an error cleaner, which, along with the anti-virus software, is a useful tool for everyone's computer. The information about windows could (and does) fill many books, but i'm sure you'll discover these few paragraphs will more than suffice to assist you in clearing up your computer problems.