Port Forwarding not working in XP

Hi,

I have a Win2K Pro laptop (internal IP 192.168.0.5) with a webcam, serving
up its output on port 8080.

This is connected wirelessly to a desktop PC running XP Pro (internal IP
192.168.0.1), running ICS and connected the the net through Freeserve
Broadband via a Speedtouch USB Modem.

The laptop can access the internet fine.

The desktop can view the webcam using http://192.168.0.5:8080

But I can't access the page from the internet using http://81.77.x.x.:8080
(or whatever my external IP is at the time).

I've tried setting Port Forwarding on the desktop, but am having no joy. Any
idea how I should set it up?

Thanks,

Fred.

Update:

OK, I figured maybe it wouldn't work from my internal network, and tried
http://www.proxify.com - lo and behold it works.

Can someone explain the logic behind this?

Thanks,

Fred.