I have two macs in my house. One has a 750GB drive on it for backups, plus its normal disk. It had been setup for Time Machine before and was working well. I also have a MacBook Pro that needs to be backed up. I didn't want to swap the disk back and forth between the two, since that would significantly erode the value of Time Machine's automatic backups. I didn't see any place where this was well documented, so I thought a quick note would be helpful to people. Most of the references I've seen have talked about different hacks to make this happen, or that it is only on a specialized Apple product that I didn't have.
I'm running Mac OS X 10.5.6 on both machines.
First, I went to the store and bought a 750GB drive. I plugged it into the mac mini that I have sitting on my desk. I configured it for Time Machine on the Mac Mini. I did a couple of time machine backups.
Next, I exported 750GB disk using the 'Sharing.' I clicked on 'File Sharing' tab to enable it. I clicked on the '+' button under the "Shared Folders" menus. I selected the volume that I had setup for Time Machine. I made sure that I was sharing via "AFP" in the "Options..." dialog.
Once I had things shared this way, I went to the other mac. I went to "Finder" and selected "Go->Connet to Server.." tab. Here I explicitly typed "afp://ipaddr/" and connected. Once I was connected this way, I proceeded to enable Time Machine. The remote disk appeared on the list of choices, so I just selected it and started it up.
I discovered that I have a 100Mbps switch, rather than a GigE switch. This made the initial backup very slow, on the order of 10GB/hr, which means I'm looking at a 10 hour backup time. Maybe it makes sense to head off to staples/best buy to get a GigE switch to plug them both into.
I've not tried to do this wirelessly, so I don't know how painful that will be. I've also not tried to connect this to the Samba server that I have running FreeBSD. I can normally see that volume on the macs without needing to do the manual step.
UPDATE: A GigE switch does help quite a bit. It was more like 6GB/hr with the 100Mbps switch, but with GigE I'm getting about 22GB/hr... So I have about 3 hours left in the backup now... 22GB/hr is about 6MB/s which seems way too slow (the hard disks are limited to about 15MB/s on each side, and the network to 125MB/s, so why the fall off in speed).