SQL Server Magazine has done some wonderful work in developing a new system view map for SQL Server 2005. A hard-copy of the map was included in a recent mailing of the magazine. But what's a person to do if they don't have a subscription? First, get a subscription! (grin) Second, check out this resource:
If you've been with SQL Server for a while, like I have, you can recognize at a glance the evolution and growth of SQL Server as a product simply from its metadata maps. The earliest maps were quick and simple. They could be grasped almost instantly and it realistically didn't take a lot of work to lay them out. I can remember doing it myself using ER/Win and PowerDesigner back in the 1990's.
But as you look at the system object map and relationships between those objects for SQL Server 2005, it doesn't take a rocket scientist to tell you that this is a complex and Byzantine set of objects and relationships. It'll be hard to keep all of this valuable information in your head. So I strongly encourage you to download it (or obtain it from SQLMag) and hang it on your wall. You'll be glad you did!