Find information about host IP address?
Using nmap from MacPorts you can run the following command to attempt to identify the OS of a remote machine:

sudo nmap ipaddress -O

e.g.:

$ sudo nmap localhost -O

Starting Nmap 5.51 ( http://nmap.org ) at 2011-08-07 17:58 CEST
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000085s latency).
Not shown: 989 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
80/tcp   open  http
88/tcp   open  kerberos-sec
139/tcp  open  netbios-ssn
445/tcp  open  microsoft-ds
515/tcp  open  printer
631/tcp  open  ipp
3689/tcp open  rendezvous
5900/tcp open  vnc
8888/tcp open  sun-answerbook
9091/tcp open  xmltec-xmlmail
Device type: general purpose
Running: Apple Mac OS X 10.5.X|10.6.X
OS details: Apple Mac OS X 10.5 - 10.6.3 (Leopard - Snow Leopard) (Darwin 9.0.0 - 10.3.0)
Network Distance: 0 hops

OS detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 8.80 seconds]