If you're looking for a good Python web scraper, this question seems to have all the information you're looking for.
As for classifying whether the blog is discussing the school's stuff, that's a much trickier problem. I doubt you'll get away from having to have the results reviewed by humans. A really sophisticated scraper would use probabilistic filters--train it on blog posts which do and don't discuss the school, and let it infer the rules itself. That's fairly sophisticated, however, and from the question I'm guessing you want quick-and-dirty. I'd just put together a list of keywords, and review (and refine) the results until it's close enough to what you want.
As for identifying the authors, this is the Internet, where no one knows whether or not you're a dog (or, by extension, what school you attended). If you had a list of authors to look for you could always use them as part of the keyword search, but if the authors choose not to identify themselves (or, worse, identify themselves as someone else) there's no practical way to do it.