By now, you know that SQL Server 2000 Service Pack 3 (SP3) exists, even if you haven't installed it. However, many people don't realize that a new version of SQL Server 2000 Books Online (BOL) ships with SP3. This full refresh of BOL is separate from SP3, and you can download it at http://www.microsoft.com/sql/techinfo/productdoc/2000/books.asp even if you don't plan to apply SP3 right away.
The updates in BOL include some crucial changes. As you know, every BOL topic includes a feedback button that lets customers suggest changes or point out errors in the document. The new BOL incorporates changes that customers have suggested. The SP3 version of BOL also corrects documentation errors that customers reported after Microsoft released the previous BOL update. And Microsoft has added topics that document SQL Server 2000 SP3 functionality.
You can install the BOL update so that it completely overwrites the previous version, or you can install it beside the previous version. I prefer to do a separate installation because I can't predict when I might want to have a copy of the previous BOL version. Keeping the two copies is especially helpful with SP3 because some topics—such as "Cross DB Ownership Chaining"—are related specifically to SP3 changes. I strongly recommend keeping an older version of BOL. It won't take up much space, and it's better to be safe than sorry.
You can easily distinguish the new BOL version from an older version by looking for the title-bar text "SQL Server 2000 Books Online (Updated - SP3)." In addition, each page that contains a new or changed entry is marked with the tag "New Information-SQL Server 2000 SP3." Microsoft claims that this marking system lets you search for new information and changes. However, such a search isn't as easy as it sounds. First, the changed content isn't specifically identified. Sure, you'll know that something on the page has changed, but you won't necessarily know what that something is. Second, the BOL search function seems to be limited to 500 hits. Searching for the term "SQL" returns only 500 hits, even though the actual number of references is much higher. Searching for the tag to see what's changed in this BOL version also returns 500 hits. It's hard to know for sure how many pages have actually changed, but it's certainly more than 500.
Despite these limits, having access to this updated documentation is essential. Often, being an expert simply means being able to find the answer faster than anyone else. Don't handicap yourself by working with anything less than the most up-to-date copy of BOL.