IIS 5.5 behind Linksys www setup

Hi Guys:
I am running IIS 5.5 on a pc hard wired to a Linksys 54g router and Road Runner 
as my cable IP host.
I Might want to test  a PayPal enabled website on my local IIS setup.
Paypal's Instant Payment Notification will send a  message to a pre-defined 
page on my IIS server.
I read that I should use dns, dcp, do something called url forwarding, set 
linksys to allow port 80 and take the external ip address of linksys into the 
machine, whatever that means, get a static IP address  etc...
All because of the router firewall and Road Runner assigning a dynamic address 
to the router.
Has anyone connected IIS to the www from behind a router?
The alternative is to build, or load, my website on a production IP host which 
I now have and try to debug the Paypal IPN from there somehow.
If I had any non-gray hairs left on my head  they are all gone in the last few 
days!
Rick USA

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