If its a server on a totally difrent network, i.e, a website server then you telnet to port 80 and type in:

GET /HTTP /1.0

hit enter twice and it will tell you some valueble info like the type of server.
If it is a normal computer on your same network, get cian & abel from http://www.oxid.it and scan the whole network, it will even tell you the type of motherboard and more.