If you are just trying to authenticate a user and retrieve his data, I would use something like TweetSharp . You can authenticate users as a web application or a desktop application, and you will have access to methods for obtaining information about users, relationships, mentions, etc. This will be much faster than trying to analyze Twitter responses yourself.
Here is their documentation that shows how easy it is to use TweetSharp: http://tweetsharp.codeplex.com/documentation
Alternatively, you can continue authentication as it is now, and just use TweetSharp (with a user access token) to pull out the data you need.
Edited to add more specific information on your subject:
TweetSharp offers a GetUserProfileFor (int userId) method that returns a TwitterUser object that contains their TimeZone, image profile URL, langauge, location, etc.
source share