Okay, well unless you do something RAID based, or similar, you'll need an existing partition on an existing system/box. This is a piece of the proverbial really, the partition obviously has to have an FS on it to even begin to save files on.
You'll struggle to get a remote disk recognised as a raw device on your machine, your best bet by far is to use something like nfs or samba to mount it over a network. For me:
Remote machine has ext3 FS and the relelvant nfs server modules in the kernel. The local machine has a mount point and nfs client modules in the kernel. Mount as per
mount remotemachine:/path/to/share/directory /local/mount/point
<THE REMOTE FILES HERE>
The file /etc/exports is used for nfs sharing; there are suggestions and samples in here before you edit it.
Thats how I would go for it. That being said, don't use NFS outside a network, it is insecure over the internet