Partitioning a hard drive:
To resize (or delete) an existing partition without losing data, you will need to use, for example, iPartition:
Would strongly suggest investing in separate hard drives. When that drive mechanism dies (when, not if) you loose all your backups for all those machines. Also, you get more backup space by having a dedicated drive for each machine.
The cost per GB is the best it has been for platter based HDD. SSD is getting there, cost-wise.
I use a base of four inXtron pleaides combo (FireWire 400/800, USB, e-SATA) that does a brilliant job for our array of macs. BYO HDD.
Coriolis systems make some great software though. iDefrag is favorite of mine.
You could look at something like Time Capsule or similar to backup the two snow leopard machines to the one device, and leave the Tiger OS machine on the current WD MyBook.
Thanks for that, which is useful, but I haven't got an answer to my initial question whether it's actually necessary to create a separate partition at all for backing up two Macs with the same OS (Snow Leopard) in the same partition, ie whether they will automatically and cleanly fall into 2 separate folders or whether there is any risk of crossover.
This is something on which I've had contradictory information and I'm trying to get a definitive answer.
There is plenty of spare capacity on the 1TB drive so I'm looking to making the most of the equipment I have rather than shelling out on a load of separate drives.
Thanks - NickR
AFAIK, you will have to create separate partitions/volumes for each Mac. Otherwise, everything gets thrown in together.
I may be repeating what has already been said, but backing up an internal to the same internal is a crazy idea. The main point of a backup is to have redundancy in case of drive faliure, which can happen at any time without warning.
Backing up several Macs to different partitions on the same external, while not preferable, is at least not as risky.
I re-read and see you aren't backing up to the internal. However, you should know that WD My Books have a terrible reputation for reliability and many or most won't boot a Mac from a clone. I would be very wary of trusting my data with one. The drives are fine, but the chipsets in the enclosure are complete junk.