Thanks for the advice buddy but I nailed the problem, just about to screw it!

U c, by making the modem itself as a PPPoE dialer, what we do is we ask the modem/gateway to connect to the Internet. Now these devices can have their own IP so every time it connects/disconnects and gets an IP, it gets for itself. It shares the connection with all the devices connected to it via LAN, thus static IP for those devices and dynamic for the PPPoE dialer. Now the no-ip DNS update, it is supposed to be happening on the PC's IP but as there is none, it won't work so in order to do so I'll have to create account at DynDNS.org, who's service is natively supported by the modem and then use its account as DNS updation service from the modem itself.
I'll update u more as I proceed and will let u know the end result. It was just a piphany that I had while driving in the noon today, yet to verify its substance.