Originally Posted by Diligent

Just get some used (=cheap) stuff to build a "file-server", give it at least
256MB so You can install Windows on it.

It's probably enough with a normal sized tower case to fit at least 5 harddrives
in it (You can get a few cheap HDD-racks to mount them in the 5.25" drivebays).

And if the motherboard doesn't have enough connectors for 4+ drives,
just get a cheap ATA133 or S-ATA controller (PCI-card) for more.

Then, as long as there's ethernet/network in the machine (built-in or a PCI-card)
You can plug it up to Your router, configure a bit and let it go to work.
Imagine 5 * 300GB-drives... *drool*