1) It seems like Spotlight generated too many files within 1 hour. How can I setup so it will generate 1 file per hour?
2) How can I view the XML file? I tried Internet Explorier (IE) but it showed the code instead of graphic.
These files are used internally by Spotlight and not meant to be viewed apart from the Spotlight History Browser. There is no way to change the number of files generated, and you should only view the previous history from within Spotlight (e.g. go to View | History Browser).