I have a document library (MOSS 2007) that I want to try to make more easily searchable. Is there a way to "tag" the documents or something, so when I search for, say, "report", I will get all the documents that have to do with reports?
you can look at the following it will help you out to understand how the search function works with crawling!
Use crawl rules to determine what content gets crawled (Office SharePoint Server 2007)
Limit or increase the quantity of content that is crawled
good place to start:
SharePoint 2007 - Creating custom search scopes
hope it helps :)
Best way to achieve this is to use search scopes. A good article on this: http://blogen.siderys.com/2009/02/creating-scopes-for-search-in.html
Further research on this should show you how to narrow results to a specified document library.
Go to link, you have a idea to create Meta Tags and quick to get Related Documents.