MBP says LaCie FW HDD is "unknown device"

My wife recently switched to a MB pro running Snow Leopard. We are both lifelong PC users, so I'm not familiar with the idiosyncrasies of the Mac H/W or OS.

I got a new Lacie triple interface rugged HDD to use with Time Machine. I plugged the drive into the FW port and formatted for the Mac (one partition) with LaCie's software as instructed. The drive became visible in the Disk Utility and I proceeded to configure and run Time Machine with the LaCie as the target. After an hour the backup (55GB) was complete. So far, so good. I then clicked on the up arrow next to the LaCie drive in the Disk Utility. I assume this dismounted the drive.

No matter what I do now, the drive shows up as an unknown device in the Profiler and of course is not visible in the Disk Utility. I have rebooted with the disk attached and also hot disconnected and reconnected it using both the fire wire (original connection) and the USB port to no avail.

1. Is the something I have not tried that might help, or do I need to send it back to LaCie? Recovering the data on the LaCie drive is not necessary at this time.
2. What, if anything, did I do wrong? (I did NOT unplug it until after I had the problem of not seeing it).

TIA

Use Disk Utility to erase and reformat the drive once more to see if that gets it on track again. Never unplug a drive without first dismounting it. To dismount a drive in OS X, right click and select eject or drag the drive to the Trash.

Does it show up if you plug it into your PC?

Does not show up with USB on PC

No, it doesn't show up on the PC using USB either (no FW on my PC).

LaCie says it's failed hardware - replacing with new

I tried using LaCie's online service ticket system with poor results. I got answers that indicated that the person on other end either wasn't reading my inputs and/or had poor troubleshooting skills.

I got fed up and called LaCie support over the telephone. I immediately got great service from a tech that understood, asked a few questions, and made the diagnosis (the bus controller in the LaCie enclosure probably failed). He hooked me up with customer service rep that had new drive shipped same day via expedited shipping. CSR also provided a return tag for my failed drive. Happily, a bad experience was turned completely around.