Thanks for the extra information Victor Tango.
I think SD may be onto something here. I know it involves some extra outlay, but I wonder if an investment in an external hard disk drive might be the way to go. The existing programs may be hung up on the backup media being too small (memory stick) or (relatively) too complex (writing to a DV or CD).
Mixture is a great advocate of backups for all occasions. I'm sure he will assist with good advice when he's able.
Other suggestions as offered need also to be considered, but I'll stay with the suggestion of an external HHD to start with ...
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