uses DOS telnet its just as good as any program you can find, but for that program:
to find out what ports are what go here
http://www.iana.org/assignments/port-numbers
telnet is 23 (for telnet servers)
echo is 7 (echos back what you send)
daytime is 13 (gives the time and date)
qotd is 17 (a qoute)
chargen is 19 (generates random characters)

for your terminal vt100 is more than adequate.

anyways your not gonna get that much out of telenting into yahoo if your able to using you program specify port 80 and connect to yahoo, then type:
GET /HTTP1.0\
that will give you the http data(html) from the webserver.
If not go into DOS and type:
C:\>telnet http://www.yahoo.com 80
and then give the same command to get the same results.
Telnet is pretty raw it establishes a connection. Then whatever you type in is what it sends. Thats why it is easy to to hand communications with simple servers try telneting to some open SMTP server.
C:\>telnet smtp.comcast.net 25
220-smtp.comcast.net -- Server ESMTP ("Comcast Messaging System - 02")
220 Unsolicted bulk mail prohibited; spammers will be prosecuted

you'll get a message like that but its ok, your not a spammer. Just type help to get a list of available commands.

Telnet is mainly used as a terminal to connect to UNIX machines. Find a free shell provider and learn how to use UNIX commands.