This question is very broad. In particular, which features are of particular interest to you? What are your goals and objectives? Are you interested in a theoretical comparison only? Do you have business goals that must be met?
Both are operating systems that are used by a large user base. Windows XP has a huge commercial software market behind it. Linux does not. A Google search for "comparison Windows XP Linux" returns a large number of links, many of which provide useful insights. Here's an example.
This was first published in July 2004