An early alpha version of Longhorn was leaked earlier this week, so that's why there is so much talk about it these days. The new file system is rumored to be called WinFS. I don't know much about it.
I read that there isn't supposed to appear any server version of Longhorn before 2005 or 2006. In the meanwhile, WinFS is rumored to be slowly ported to Windoz .Nut Server 2003 before Longhorn Server arrives. I'm not one in the know though, so that's why I used supposed and rumored.
Gary should be, like usual, the one with the most accurate information about the upcoming Microsoft OS.