Windows Vista offers an option to name your PC which is used when your computer joins a network. It helps to have something descriptive, however if you bought an off the shelf PC this name might be set to something cryptic already.
Changing this to something better is easy to do. First press WINDOWS KEY + PAUSE to take you the system information panel. Then click on the Change Settings text next to your existing computer name:
In the system properties panel, you can assign an optional computer description and then click the Change... button to select a new computer name:
In this window, type in the new name you wish for your computer and then click OK. After this, you may need a restart, but the PC has been successfully renamed.