SQL will not connect using external ip

[frosty90]

I have setup SQL 6.5 on a machine. I have verified that port 1433 is opened for SQL. I am also using a router dell 2300. I am running Windows XP.
I have set up my machine to port forward and have setup a static ip 192.168.2.136 nothing I do seems to work.

I can connect to the server by name

ex:
conn.Open "Provider=SQLOLEDB;Server=YOUR-588B4A13EA;User ID=test;" & _
";Password=user;Initial Catalog=test;Network Library =dbmssocn"

I can also connect using internal IP address

ex:
conn.Open "Provider=SQLOLEDB;Server=192.168.2.136;User ID=test;" & _
";Password=user;Initial Catalog=test;Network Library =dbmssocn"

but when I try to connect to the external IP 12.216.xx.xx
I get the dreaded sql does not exist error.

I have tried to register the server using the external IP but the enterprise manager gives the same error. SQL cannot be found.
I am not sure what I missing.
Thanks in advance for any help
Chris