I recently bought:
"Microsoft Exchange Server 2003" written by Walter J Glenn and Bill English. It is the 625+ page version. (Blue cover)
I am needing to design a solution using security certificates, i have found this book to cover this area very well. I looked at a few others after this one, but found the depth of info in this to be the best.
Goodluck
"Assumption is the mother of all f#%kups!