Hi

Another great product is nessus www.nessus.org
The product only runs on versions of *nix but has good support, is open software, and is free.

There are lots of support info on the WWW, and you can download new vulnerability plugins as they become available.

It will scan single IPs and ranges for various open ports, OS information etc, etc

PS you can also download a Windows client for it to!

Golam