The battle.net text gateway was shutdown years ago so BNX is not usable except either by using a battle.net clone that implements it (e.g. XGN, FSGS, etc...) or netcat.

To use it with netcat have netcat listen on TCP/IP port 6112.  When BNX sends its username and password, you should respond as follows:

2010 NAME username

This tells the bot it's unique name (e.g. battle.net ensures the name is unique by appending numbers at the end in the event of a collision).

Next, put the bot in a channel...preferably the channel in bot.cfg.

1007 CHANNEL "channel name"

Now make the bot aware of itself in the channel

1001 USER username 0012 [CHAT]

The 0012 is a bitmask...the meaning of the bits aren't important.  Just note that it means the bot is the channel operator (if it's not, you can't see it do some cool things like splatterkick or voteban)

Now, you'll probably want to have some users join the channel. 

1002 JOIN someuser 0010 [CHAT]

Similarly, a user may leave

1003 LEAVE someuser 0010

To make the user talk

1005 TALK someuser 0010 "someuser's message"

The bot percieves this as chat in the channel.

If the user wants to send a whisper to the bot

1004 WHISPER someuser 0010 "someuser's message"

This should be enough to allow you to play with BNX.  Be sure to read BNX.TXT.

P.S. Keep in mind, you're essentially emulating a battle.net server...a user does NOT actually communicate with the server in this manner.  The server generates this protocol.