Again I can't say 100%, but it makes sence for Microsoft to allow for easy migration. You should be able to export from Outlook express, and import into "Windows mail". Outlook express is replaced by Windows mail in Windows Vista.
If you're looking for a new server from Microsoft you'll have to wait until the end of this year. That's when they will be releasing what is now known as "Longhorn [microsoft.com]". Most likely it will be named Windows Server 2008, but this has yet to be confirmed.
Vista is fine for development, but it's hosting capabilities are limited.