OK it is my turn now, I have to correct myself 2, In adition to what I suggested in my last posting as a solution, beside the router, Noname added another fix, that is the PC to be used as a login method to the ISP using PPPOE, I have to say here though that I have done that very briefly only on XP PRO pc but the tricky part was with the ports and traffic you allow back towards your internal network behind the PC which is tenor at this point.
But again router is the easiest fast fix, try that first.
Hwyking