This is how I have established network between my PC and my laptop at home (being novice in networking, it took me few days to achieve the feat). And it is working perfectly. I can easily share files between them.

Laptop

IP Address: 192.168.1.4
Subnet mask: 255.255.255.0
Default Gateway: 192.168.1.2

Desktop

IP Address: 192.168.1.5
Subnet mask: 255.255.255.0
Default Gateway: 192.168.1.2

ASUS RT-N10+ Router

IP Address: 192.168.1.4
Default Gateway: 192.168.1.2

I have connected the Desktop PC to the router using a LAN cable, and laptop to router over WiFi. Both, PC and laptop are running on Windows 7 OS, are on same HomeGroup, have same username / password. Also, I have connected the Ethernet cable to LAN port 1 of the router.

Click here to view a graphical representation of the network. Can't post image here, because I don't have 10 reputation points.

Now, what I want is use connect to Internet using a 3G USB modem on one device and share it over the network on the other. I tried Huawei and Micromax 3G USB modem. Both obtain a new IP address whenever I connect to Internet (means they have dynamic IPs). Rest, both have Subnet Mask as 255.255.255.255 and Default Gateway as 0.0.0.0. In that case, I cannot directly share Internet from the modem. Preferred DNS is blank for now in both, laptop and PC.

What I am planning to do is to connect to Internet on laptop using the 3G modem and share the Internet connection over laptop's Wi-Fi (as hotspot) using Connectify, which I have done already. That, I suppose, will broadcast a static IP to connect to.

Now what I can't figure out is that what changes should I make to the network settings of the router and the PC so that PC connects to the Internet broadcast by Connectify? Is that possible on the first hand? Please note that I am trying to implement the network without spending anything extra (for purchasing as USB WiFi adapter for PC, of course, which could have made the life lot easier for me).

Thanks in advance