If you have PCI slots open, you can probably get a USB card for around $20 - $30 (US), maybe a little cheaper. I don't recall mention of what OS you're using, but the card should come with drivers for anything likely - but check that out before you give them the money. Get USB-2 if possible, although with a little loss of performance a USB-2 drive should run from any older USB port - just a little slower.

Of course, that's if you think an external HD might be handy, or are thinking about digital camera, or ... .

If you have an older machine, a 20GB or so HD might look enormous compared to what's in your current machine; but any new machine you might want to carry it along to will likely have something more like 40GB or 80GB (or even much larger), so shoot high if possible. Externals smaller than about 30GB aren't commonly on the shelf in my area, but the smaller ones are somewhat cheaper. Your choice.

Jon -

Quite a few folk talk about using camera cards as a substitute for floppies. I don't know many who actually do it much, since everybody's "connected" and you can email a file quicker than carrying it down the street. A card reader is around $20, typical, and you can take it along; but the cards are not a good way to archive stuff (they will eventually self discharge on the shelf - usually weeks, not years) and a "useful" size - 64MB to 128MB - card is nearly the price of a 60GB external (portable) hard drive, in some formats. Of course, the hard drive doesn't fit in a shirt pocket very well.

As a "sneaker net" utility, they're fine. There are a lot of cheaper and safer ways to store anything very large.

John