When the subject of which version of Media Center someone is running there is often some confusion - this is because the version of the Media Center software and the Windows XP version are different. To identify the version of Media Center you are running do the following:
If the version displayed is not "Windows XP Media Center Edition 2004" you're not running the 2004 release - contact the manufacturer of your PC (i.e. HP, Gateway etc.) and ask about getting an upgrade.