I'm with WS, though additional HDD's are an even better option. On the PC side, 40 gig IDE drives are readily available for under $150, and that's a bunch o' CDs with a read-write speed a quantum leap over any back-up solution.
Jazz media aren't actually disks, they're tape cartridges, so they're desperately slow. Zip and Jazz were viable solutions 3+ years ago, but with decent CDR-W and up-and-coming DVD-RW, it doesn't make sense to invest in a proprietary media format that's slow.
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"The problem with the world is that the ignorant are cock-sure, whereas the intelligent are full of doubt." - Bertrand Russell