There will be no Outlook Express 7 to go along with Internet Explorer 7. Instead, Microsoft is replacing OE with "Windows Mail," which is basically the same client with some minor changes. It, however, will only be available for Windows Vista.
On both Windows XP and Vista, though, you have the option of downloading Windows Live Mail Desktop, which is currently in public beta. It is considered the replacement to Outlook Express for XP users and an upgrade from Windows Mail for Vista users.
The one thing I can't understand is why Microsoft would develop two separate clients for Vista, one that has exactly the same functionality as the other and then some, which are both free, and intend one to be an upgrade from the other. It just doesn't make sense.
John
After reading all I could about the new browser, I have a question. Can anyone tell me whether Outlook Express was upgraded along with the browser, or is that still going to be OE6?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic