The IP address is logged by the web server, you just need to get access to those log files from your host. You can use the navigator object to get other miscellaneous information about the user's environment (OS, Browser...) but thankfully the browser won't provide you or anyone else more personal information such as names, addresses (land and/or email), phone number or the like.
If you want that information, you'll have to ask the user to provide it but first you'd better be sure you need it. Also explicitly state exactly why you need it, all the uses you'll make of that information and exactly how privately you'll handle that information.
Personally if I hit a site that needlessly requires personal information I fill the fields with snide comments and garbage entries.