Get response from telnet server with putty, but not with Arduino telnet client

Those funny characters are the telnet server asking you a few questions. A 255 (0xff) byte is IAC (command start), the next byte is a command, and the third is an option. Some are explained here.
http://support.microsoft.com/kb/231866

You need to respond to those first. I should have warned you about that.

Google search "telnet IAC" for more sources of info.