Free IT Network Health tool

Preparation Wizard is great free tool that was developed by Microsoft Essential Business Server team (http://www.microsoft.com/ebs/en/us/overview.aspx ) that scans your network,  identifies various networking problems (DNS, AD replication, AD configuration, configuration of network adapters, etc.) and provides links to knowledge based articles that explain how to correct these issues. 
The tool is not just for customers with Essential Business Server or those who are planning to deploy this solution in their environments. Preparation Wizard is for anyone with Active Directory in their network who would like to verify the health of their environment. The tool runs over 100 different checks which are based on most common issues resolved by Microsoft Customer Support Services over the past 10 years!
The tool is specifically designed for mid-sized networks (25-300 PCs). Preparation Wizard does not change any settings in your network, so it is safe to run at any time.  Unlike many other known tools which simply dump large amounts of networking data collected from a single source (such as event logs, for instance), Preparation Wizard is able to gather data from many different areas( Active Directory, DNS, SYSVOL, event logs, etc.), cross reference that data, and make conclusions about the overall health of the network.
Go get it – it’s FREE!
http://www.microsoft.com/ebs/en/us/preparation.aspx