Information about Windows update KB923689
"I have installed Windows Media Player 11 on my computer. Why am I being offered the Windows Media Player 6.4 security update?
While Windows Media Player 11 is not vulnerable, Windows 2000 Service Pack 4, Windows XP Service Pack 2, Windows XP Professional x64 Edition, Microsoft Windows Server 2003 or on Microsoft Windows Server 2003 Service Pack 1 and Microsoft Windows Server 2003 x64 Edition will still have Windows Media Player 6.4 installed on the system for backwards compatibility."
Information about Windows update KB923694
"A remote code execution vulnerability in a component of Outlook Express could allow an attacker who sent a Windows Address Book file to a user of an affected system to take complete control of the system.
If a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less affected than users who operate with administrative user rights."
I would install them both.