I Got It Working
I used the command line hack to enable unsupported disks.
First, the setup:
I use a MacBook Pro 17, with Gigabit Ethernet. I have one external 80GB FW800 Drive.
After careful deliberation, Time Machine declares that I have 1.3 million files in need of backing up (first time), at 127 GB.
I have an Airport Extreme Base Station, connected to a 1.3TB Drobo. The
Drobo is an ideal network drive, as it is a "Slobo." It ain't exactly a racecar. However, it is very, very safe, and offers RAID 5 reliability at a fraction of the price.
I connected the Drobo to the APE Base Station, then the APE up to my network, turned off the wireless (security -call me tinfoil), and hooked up the GB Ethernet to my laptop. I have the share being advertised using Bonjour, with account permissions.
I have to mount the drive (very easy in Leopard). I use Time Machine to select the drive.
The first backup is a doozy. It is critical that you let it go from start to finish in one swoop. I tried breaking it up into parts, and that never worked. In my case, it took two days over GB ethernet. I don't even want to THINK about how long it would take over even 802.11n.
Another critical aspect is that, however you connect for the first backup is how you need to connect forever afterwards. I tried connecting to the backup via wireless (just an experiment) after the Big One, and got reset to the beginning. I have to connect by wired Ethernet from now on. I can live with that.
In any case, it now works. It ain't fast. Time Machine is not efficient at all. My wife's computer uses a FW800 to connect to a 750GB LaCie, and that is a decent speed.
YMMV.