If you're just talking about running Crystal on your local machine and generating reports, that's fairly easy.  When you create a report, you are prompted for a data source.  One of the options is XML.  Just point the report at your XML file and schema file, and you're good to go.

If you're talking about integrating a report viewer into your application, where users can generate their own reports, that's a bit trickier.  I recommend checking out Ken Hamady's site for a viewer.  You will likely have to pay some licensing fees to have it up on a web server.