Internet Sharing/Networking Woes (Today's puzzle to solve)

[Zargo]

Ok so here is a puzzle for everyone to solve today. So First let me present you with the problem.

Supplies:
1 Linksys Router Model Befsr41
1 Westell Dsl Modem
4 Computer Addicted WoW Players Each with their own computer
1 House
Bellsouth Dsl Extreme package

I Know the basics of how everything works so for the sake of things lets assume that I know which cords go where. nothing wireless all on ethernet. All 4 pc's on windows xp.

The router itself has 4 ports and an internet port. If I hook my pc direct to the dsl modem The internet works for me (how I am currently talking to you). Just direct connection. Basic Easy. Ok we know the dsl modem works.

If I connect my pc to the linksys router and ping it. I get the Login prompt. I get into the router interface ect ect shows I'm connected to router. Ok that's clear we know the router works.

If I connect my DSL modem to the internet port on my router. I can connect to the router like normal ect. but I can't connect to my Dsl modem. But that's just problem 1. This is were things get weird for me.

If I connect myself and/or 2 other computers to the router and put the DSL modem into a Regular Port on the router. All 3 are connected to the internet and everything works.

Doing it this way would be fine if I only wanted 3 connections, but I need the 4th port. Why will 3 connections and my dsl modem work in the 4th port, but
my dsl modem won't work in the internet port so i can use the regular 4 ports for all the computers? This is really starting to get annoying. 3 of us have the net which is good but I want the 4th working as it should in the 4th port and the dsl modem working through the internet port and not a regular port.

So why is my dsl modem working ok in a regular port now but it's not working in the internet port of the linksys?

Just kinda boggles my mind. Any of you guys that are willing to help me with this would be great. I just don't get it. More then likely it's something simple i'm overlooking or something in the software i need to change or something. It's usually something simple that causes the most problems.