General support for Outlook Express on Windows XP ended on April 21, 2010.
Outlook Express 6 Security Fixes Through 2014
That means security updates will be available free from Windows Update at least until April 8, 2014. Other new updates such as service packs and hotfixes are not available.
Paid phone support for Outlook Express 6 and updates to the Microsoft Knowledge Base will be available through April 8, 2014 at least.