DNS timeout

Good day,

please, help me solving this,
i configure a server( ubuntu 8.04 ) that connect in other server, this is what i want to do..

named for the clear explanation.
computer connected to server(o) : xoxo
server i configure: server(o)
server i connected: server(x)

i want to connect to server(o)comman d nslookup to see server(x) but the reply is dns timeout, but when i ping the server(x) using xoxo it alive.

i tried to check all the possible cost but i cant find the problem. thank you for the help.