We are going to retire a machine that has been out faithful domain server for 15+ years running Windows 2000 SBS. We no longer need a file server, nor a domain as almost all of our applications are now cloud based or use peer-to-peer networking.
Users will be migrated from authenticating on the domain, to authenticating on their individual workstation. There are only 10 active users so user management won't be a big issue.
We will still need central file storage. This may end up being a Windows 7 Pro workstation with lots of hard disk space or perhaps one or more NAS systems. There does need to be varying levels of security on file storage. This can be user based.
We will need to maintain compatibility with many versions of Windows. We have a legacy application that is rarely used, but when it is it requires a Windows 98 machine be brought on the network for short periods of time. There are a several users who won't let go of their obsolete XP Pro machines, The balance of the user base is Windows 7 Pro and Windows 8 Pro. Some Windows 7 and 8 Home edition as well which currently don't authenticate via the domain (since they can't).
I'm pretty familiar with peer-to-peer home networks, but this need goes beyond simple networking, just not as far as domain networking.
I'm open to suggestions as to the best way to approach this. 500 Points will be shred among the best 5 or less responses.