I personally use HFS... It is a great, free Web-server that is a single executable file that offers user log-in access, many user accounts, uploading, downloading, and you can even customize the HTML Template. Try it out, it's free. As for the hard-drive, you'd be best to find some sort of NAS enclosure like the D-LINK DNS-232 (I hear is not amazing, but is a good example) that offers Gigabit LAN, and USB, and also RAID so you can use two 1TB Hitachi's or something. Hope this helps!
DG6464
Note: The expensive NAS enclosures offering RAID also generally offer some sort of HTTP or FTP based web access. I personally like to use my machine as a gateway to the box through HFS or Apache. Just map the drive as a shared drive on the PC, set it up as a virtual drive in HFS, and set user account access to it. I also use HFS to link to my VNC server through the Java option. It's a great all-around free solution for software.