Microsoft Outlook is part of Microsoft Office.
Microsoft Outlook Express is part of Windows 95,98,ME,2000,XP. It was replaced by Windows Mail in Vista but is basically the same program.
Outlook has lots of features, email is just one of them. click here
Outlook Express is for email and newsgroups and that's it - it was left behind on that front a long time ago by freebies such as Mozilla Thunderbird. click here
You can install a calendar add-on called Lightning into Thunderbird which will do what you want; click here
I ought to mention Sunbird too, which is another Mozilla product - but I've never actually used it, and it's still yet to reach version 1.0 - click here