Cannot Connect RDC thru Dial-UP Modem

Hello and thanks in advance.

Here is what I have done thus far.

1. Configured Host Computer with IIS. No prob
2. Configured Host Computer with my own Port #. No prob
3. Configured Router to Forward My Port# & Port 3389. No prob

I can connect to my computer at work from another computer & visa-versa ex:
my co-worker comp to mine and mine to my co-worker comp. By the way we are
on DSL here at work. So my issue is when I disconnect my DSL and connect to
the internet thru dial-up modem and then try to connect to my co-workers comp
thru the IE browser it seems to be searching but nothing happens.
Here is what I did.

http://co-worker IP:co-worker PORT/tsweb

Then I tried something else was to enter our Router Gateway IP instead of
co-workers

http://Router IP/co-worker PORT/tsweb
This time the Web Log in Box showed, I clicked CONNECT and it tried to
search but then I got an Remote Desktop Disconnected error.

Hope someone can help me out on this. Hard to find answers on the web.
If more info is needed please ask.

KJG