The server can run fine on Vista / Windows 7.. that isn't a problem.. it is the SFC OP client that suffers on the Vista / Windows 7 OS.
Server = good to run on Vista / Windows 7.. absolutely 0 issues.. it actually runs better on the 64 bit OS.
game client = Needing XP to play on a live D2 server for hex flipping..
Other than that.. game client can be used for DH's turn based idea without issue.
Game client on Windows 7 / Vista can also play single player, TCP/IP, and GSA without issues.
As for Server Kit.. it loves Windows 7, Vista (even more on x64 versions).