I need a little help with backing up files; photographs and graphic design work. My iMac has only 60GB memory so I need to empty it regularly and have just got a 320GB external F/W drive for this purpose.

I use a folder called "Folio" which contains 2 folders called "design" and "Photos", both containing 100 files(example). I back them up to external HD (and CD) and remove from main HD. Now I create 10 new files in both folders so I need to be able to ADD them to the existing files on the external HD without affecting those files and keep the new ones mirrored with the main drive whilst working on them. Ultimately deleting the new files from the main HD when completed as before.

Make any sense? Is this incremental backing up?

I don't need an app that gives me earlier versions and dates aren't important. Any ideas?