What to use to keep separate versions?

[dbates]

I'm a big user and supporter of SuperDuper. I installed it for a client just recently to clone her main hard drive, and of course, it worked very well.

However, she wanted me to be able to back up a subset of files on her hard drive (it wall probably be the Users folder, but maybe just a folder called "Clients") to an external drive, but when the program backs up, every time it encounters a file that has changed, instead of overwriting it, the program adds the file, and also keeps the original, perhaps creating a dated folder to store the original files.

What she wants is to keep every version of every file that has changed so she has access to them, until the space of the hard drive fills up.

Of course, what I'm describing is Time Machine, but she's a graphic designer, and is a little skittish about upgrading to Leopard just yet.

So, I guess what I'm asking for is your opinions of software that is hopefully as good and reliable as SuperDuper, but includes more of the Time Machine functionality, so that I can use them together until she upgrades to Leopard.