So you've set up a home network and you've connected a bunch of desktop at your home to communicate with each other. However, you're stuck with two problems:

Problem 1: Searching for files across your network. If you're a tech addict like, you probably buy a new desktop yearly. Good news is that you've used your old desktops to connect every room in your house, bad news is that you really can't remember which PC you've saved some of your files.
Solution: What you need is a LAN search tool that will allow you to search for files across your home network. File-O-Scope is one software which can do this for you, plus you can also make a playlist out of the MP3 files saves across your home network.

Problem 2: Since you have a bunch of PCs in your house, every family member probably has their own PC and when you're all using it at the same time, it's a pain shouting at each other across your house.
Solution: Aside from using free email to communicate with each other, you can also use LAN messaging tool. If you're running OS X on your PC, you can use iChat or LANMessage.