Have you considered that people may not want to give you their computer name?
This is the most important part in a discussion like this. You are given a very limited ability to discover details about your visitors for a reason: security. If any web server could load details about their clients, such as details about their network setup, it would make it that much easier for them to mount malicious attacks, or violate their user's privacy.
If you want such details about a client, you will need to get them through a client-side application. For that you need languages like Java to be installed on the client, which gives you the ability to *request* permission to access the client file system or execute system commands. The user can still deny you access, though.