Strange that the LaCie drive doesn't work right with your 8600. My guess it that it doesn't like the USB 3. Does it work with the iMac G5 running 10.5.8? Is it formatted correctly? I don't think OS 9 has support for NTFS disks.
Have you tried the Target Disk Mode suggestion made by Swampus? That might be best. And may I be as bold as to ask the name of this magically awful Apple retail store so that I may not visit it?
USB 3/2 didn't have anything to do with it. Turns out that the old G4's aftermarket installed PCI expansion card is so old it's a USB 2/1 version, but the USB 3/2 drives work just fine on it anyway. Read on!!
Went back to the Apple retailer (MacOutfitters, Cranberry, PA) with the drive. Box does say OS X10.6.8 and up (Intel) but, when pointed out to the store salesperson (who happened to be the "store manager" - less than 30yrs. old) his reply was "Oh that... yeah that means that the included software for formatting the drive plus drive utilities wouldn't run on anything older than 10.6.8." I said really???? You mean to tell me that i drove back out here (after having called the store yesterday about this and was told to return it) - about a 25 minute drive - only to be told that it really wasn't an issue after all?
Whole thing is kind of funny/stoopid/moot point anyway. This Apple retailer's store sits RIGHT NEXT to a mall that has a BestBuy in it and I had stopped in THERE first before returning the LaCie to the Apple retailer to see what was available.
Lo and behold, they had Western Digital 1TB Passport drives on sale for $69.95 ($10 more than what I had paid the previous day for only a 500GB drive from the Apple store that was advertised as on sale from $69.99 to $59.99).
A quick call to WD while in BestBuy verified that this Passport could in fact be formatted under OS 9, have the files transferred to it and then re-transferred to my newer iMacs.
1TB for $69.95 vs. 500GB for $59.99/$69.99??? NO BRAINER!
In the meanwhile, since I started this thread, I've successfully networked the old PM8600/G4 to the iMac via an Ethernet cable and even THAT works like a champ now using the old G4 as a server. THAT G4 still has 2 more drive bays in it that could take older (but still large) hard drives for an additional RAID storage array - I HATE throwing out things that are still working perfectly even though they're just "older" than what's on the market now.
But as for this MacOutfitters retailer, if I need anything from them in the future I'll still take whatever they say with a grain of salt. It's obvious that all they're interested in doing is pushing product out the door.
Bill