Help Me Regarding Lan Networking

Hello,
There Every Body, i am stuck in a problem and need your guidance i searched all forums but no help so Far. :(
I have a laptop and DeskTop, My Desktop is connected to Internet through DSL and my Ips are:
192.168.1.2
Subset Mask: 255.255.255.0
Default Gateway: 192.168.1.1

Now my Desktop has only one Ethernet port, which is connected to DSL CPE. While i want to setup a network for file, internet sharing with laptop. So instead of buying a new LAN card, i got a DB9 serial port to RJ45 Ethernet Converter cable and connected the serial port (COM 1) to by Laptop Ethernet jack, but still i can't establish any network.
Please can anyone guide me step by step through the whole Setup.
I am not good in networking :(
Thanks