I don't know if this is in the right section, but here goes:

My client has got two laptops: for this, I will call them Laptop 1 and Laptop 2, and a Seagate FreeAgent Desktop 500GB USB drive.

Both daughters want their uni and college work backed up.

I have created two folders on the drive, one for the backup of Laptop 1 and one for the backup of Laptop 2.

The backup works fine, but I cannot find, even on the Seagate forums and in the documentation, how to choose a specific folder. Some people say the only solution is to set the laptops up as shared, but then I think that's a bit complicated for a my client, who wants to backup on his own.

The drive uses Seagate's Drive Backup software (called FreeAgentCN.exe)

Would it be easier to use an external piece of backup software (for example Roxio Backup?)

I don't know the answer so if someone else does, please join in. I just want make sure we're all looking at the same picture.

but I cannot find...how to choose a specific folder.

I don't know what that means. Do you mean you want Notebook 1 to automatically go to Backup Folder 1, Notebook 2 to Backup Folder 2, and Dad to Backup Folder 3?

Some people say the only solution is to set the laptops up as shared, but then I think that's a bit complicated for a my client, who wants to backup on his own.

Where is this external drive attached? To Dad's Computer? If the girls' notebooks can use the drive now, then the only sharing needed is to Dad's Computer, and that would seem to already be done. Sharing should NOT, I say again, should NOT be setup on the notebooks if they will be connecting directly to a pubic or campus network.

The external drive is connected to Laptop 1, which has been backed up, but not to any specific folder, as yet. To backup Laptop 2, the external drive obviously needs to be connected to L2.

I want to backup the contents of Laptop 1 to Laptop Folder 1, contents of Laptop 2 to Laptop folder 2. Their Dad's computer is not going to be backed up, as he only uses it occasionally and not for work.

Okay - so this external device will be physically connected each time to the computer it will backup. Then no sharing is needed.

If the software for the backup program installed on each computer (check license to make sure that is legal) does not allow the user to specify a folder, then I can't help - and hopefully someone else reading has a solution. I know Windows own little built-in backup program is pretty flexible.

Sharing may actually be an easy solution, but it does weaken the security of the host computer. And since USB has NEVER been a reliable connection for frequently removed devices (hurry up USB3.0!) the easiest solution may be a 2nd external drive for notebook 2. More money is not what a dad with 2 kids in college wants to hear - though it should be no surprise. But we must remember, it takes little time for the value of the data on the computer to exceed the value (many times over) the hardware!

If they will be sharing living spaces, then a router may be the best bet, and a Network Attached Storage (NAS) (drive not included) device that attaches to router in the same way as the notebooks, without having to enable sharing. Note with a router, a networked printer can be shared in the same manner. This is nice because the NAS and printer can be located in a common area, and not tethered to someone's computer.

I set up a wireless network for him last week, so the daughters could use the laptops in their rooms, and they don't use the printer; just some more info!

just some more info!

Well, the options remain the same - my preferred is any method that does not require access to another computer. That would be separate external devices, physically moving the external device to each computer, or some form of network storage device (the best option).