Can we know the operating given the IP address or DNS of the host.
All I have is
file://myserver/myapp
Can you resolve the server name?
nslookup myserver
You could try telnet, ftp or ssh to the address. It might give you a clue in the login prompt.
Can you not trace it with the network team? From the IP address, they should be able to trace to the physical server from the switches. At least you could then see the hardware and perhaps get console access.
Robin
Liverpool/Blackburn
UK
A useful method is to use nmap along with -O flag.
Be cautious however when using nmap inside a company network since sometimes (and more often than not) they ban its internal use for anyone outside their network team... Most networking guys would freak out if they detect a strange IP scanning their network. 
In any case, there's no bulletproof method to detect the operating system flavour of a remote host with 100% effectiveness.
If you need to research the task, you can start with TCP/IP stack fingerprinting - Wikipedia, the free encyclopedia
There's not much there, but that wiki page and the phrase "OS fingerprinting" will get you started.
Regards,
Alister