with NTFS, this is build into the OS. Security at user level - group level - folder level - even file level.

You can do this on a windows 2000 or windows XP machine.

The only limitation will be that 10 users at a time can connect to that computer. If you have more users than this, then you will need to be creative about where you store the information (same info on more than 1 machine being synched between the two or more machines) or you can get windows 200X server.

Good luck

~Halv