if you want a single solution then look to overland and the snap servers.
high availability raid arrays,
you're able to put on expansion units to upgrade storage when /if you manage to fill the storage,
they can serve Iscsi disks to your clustered servers or to form a remote mail store or something so that you're data isn't stored on a physical server.
they have SCSI host ports so you can connect a tape drive to do back ups.
of course all that doesn't come cheap...
so basically your three options are
free: linux (you already said that you don't want it, and I don;t blame you, it sounds like you're a windows guy, and it's not really worth learning a new OS for a file store server!).
medium cost: windows, then use windows file shareing and NT backup comes free.
massive cost:
buy a dedicated piece of hardware. the snap server that I said about costs a few grand...
but I seem to remember seeing something that was basically a file/folder server in a single box with five removable disks in it. that could server windows shares etc, and also do Iscsi disks, ftp appletalk etc, basically everything that the snap server could do, but for the privce tag of only £1,000 -which by the time you've bought the hardware and disks etc is about the same as a decent file server anyway. -the only way that this differed from the snap server was that attaching external disks would have to be USB disks rather than scsi raid arrays or scsi tape drives, (but USB external disks are cheaper than SCSI disks anyway.
I can't remember what the thing was called though. it was literally bought during my last few months working at a company.