Will Windows Server Longhorn with Windows Vista have the possibility to configure roaming users ? This means that when they log on, they get their own desktop, files, etc.When they log off, desktop, files etc. are stored on the server. This makes that users get the same environment on whatever computer they are working.

Yes - roaming profiles are available in Windows Server "Longhorn". You can access profiles through User Accounts in Control Panel and clicking Configure advanced user profile properties. It's pretty similar to the way it was before.