For years resource kits were extremely useful for understanding changes and principles whenever new OS was released from Microsoft.
I remember 3 resource kits from past – Windows 2000, Windows XP and Windows 2003. Windows 2000 RK was extremely useful – great books and CD with extremely useful utilities, however it was pretty expensive – luckily I had one at my work ;) Windows XP RK was not that interesting – there were not that many changes in XP compared to Windows 2000, so documentation was not really needed to understand it and CD with utilities was very poor.
Windows 2003 RK was again very useful – with downloadable set of utilities, this was must have (and utilities were available for free now).
I haven’t read Windows Vista RK so far, however I always wanted to – and now it is available as ebook for free (Microsoft Press celebrates 25th anniversary).
DON’T WAIT AND DOWNLOAD IMMEDIATELY :)