With an Ethernet "splitter", you can simultaneously connect two computers (or other network devices) on one Ethernet cable. You can buy Ethernet splitters for approximately $ 20.00 USD but you also can make your own.
One office, one ethernet jack and two computers, or
One living room, one ethernet jack and one HTPC and one XBox.
If you can't realistically (without tearing apart walls or renting a scissor lift) pull one more ethernet cable from the patch panel to the office / living room etc. you can consider the use of an Ethernet "splitter".
I'm assuming all the four pairs of the ethernet cables are properly connected within the ethernet wallplate and the patch panel.
Step 1: What You Need
In order do make your own Ethernet splitters you'll need the following:
Two RJ45 Crimpable Plug
Four RJ-45 keystone jack
Short Ethernet Cable Scrap (approximately 2 feet)
The tools you'll need:
RJ45 Crimp Tool
110 Punch Down Tool
Loctite Super Glue