The advantages of a network that I know of.
1. Your computer can use and change files on another computer as if it was on your hard drive.
2. You are able to share printers.
3. You don't need to buy another internet connection.
4. The router provides excellent security.
5. You can actually run programs directly from another computer such as MS Word, Excel, Photoshop. Any program that requires very little information flow at one time can be easily run from a different computer in the network. Thinks like games can't be run like this though. I tried playing SimCity3000 from my room mate's computer and it was just brutaly slow, the game required too much information flow.
Here are some little disadvantages of a network.
1. You can't send files through MSN, ICQ or any other chat program.
All signs point to network
*fixed major grammer errors*