This content is 20 years old. I don't routinely update old blog posts as they are only intended to represent a view at a particular point in time. Please be warned that the information here may be out of date.
Network scanning tools are a bit of a grey area. For those of us who need to keep systems secure, they are valuable tools. But for those who are unaware of their existence, they are a means for a would be attacker to scan your network in search of vulnerabilities.
The eEye Digital Security website has a number of free utilities which may be of interest, in particular the nmapNT and LibnetNT utilities, which are Win32 ports of the similarly named Unix tools.
More free networking tools can be found here:
Network Management Tools
Enjoy!