In most home installations, that is not long enough. You will more than likely need to purchase a separate cable of either 50 or 100 feet for your installation. You can use existing phoneline in place. Speed up to 10 Mbps Cons-computer has to be opened to install card. Slower than traditional Ethernet.
Additional cards are expensive.
HomePlug is a networking technology that uses the existing home electrical wiring to connect your computers. This is an old approach for home networking that never caught on due to technical difficulties. The HomePlug Powerline Alliance has been working to fix those problems. You plug your network adapters into the outlets and your computers can talk to each other, no central hub and or access point is needed. This could be the most flexible of all the wired home networking technologies.