There are websites that tell about using Linux and Unix. I don’t have one to give you at this time, but I found several sites earlier using google.
As for other OS books, I have found the MCP books to be excellent. I am currently reading “Supporting Users and Troubleshooting a Microsoft Windows XP Operating System to prepare for the MCDST exam 70-271. It is a self-paced training kit with question s and practice tests also. There is a Microsoft book on server OS. I found it on Amazon for less than $40. It was published by Microsoft Press. The books are thorough showing you how to do things, followed by practice lessons and questions.