@pyrre
Yeah, spanned volumes aren't ideal (I think I commented on the limitations somewhere in that old message). You could have partitioned the individual disks and mounted them as directories, however:
C:\Data\MyFristDrive -> \Device\HarddiskVolume1
C:\Data\MySecondDrive -> \Device\HarddiskVolume2
etc.
Whether or not Windows 2000 (or any other OS) performs well using SMB/CIFS over GbE depends on the TCP/IP configuration of both the client and the server (in particular, the requisite receive window size, e.g. 1,000,000 bytes for GbE with 1ms RTT--Google "bandwidth delay product"), MTU (Windows limits the MTU to the host requirements RFC minimum when it can't do path MTU discovery across a router), which version of SMB/CIFS is used by the client, and the overall speed of the system.
Windows 2000 does not tune itself for high-speed networks out of the box. You have to do a bit of tweaking to get it there. The same can be said of most TCP/IP stacks.
Without reading from cache, you're probably not going to fill a GbE link using a single disk, especially an older model spinning at 5400 RPM.
You want a file system that allows its internal structure to be distributed among disks and loaded/unloaded as disks join/leave a disk group, dynamically updating information like display information like directory listings and free space at the same time.
EDIT: And rather than implement a NAS, you may want to look into SAN hosts (iSCSI or ATAoE over GbE is probably the cheapest access method) and cluster file systems, i.e. file systems that appear local to and can be accessed by disparate hosts simultaneously. That coupled with dynamic attaching/detaching of physical disks would be ideal, I suppose.
EDIT2: Hmmm. GlusterFS
http://www.gluster.org/. Check out the aggregation feature, which really stems from their decentralized approach. Looks very promising.