I saw this lament in my referrer logs, of all places. Perhaps someone read it, then wondered if I had an answer?

The exact solution the author sought,  a USB-IDE converter so he could attach a thumb drive as an IDE device, doesn’t exist as far as I know. But I can think of two things that are almost as good.

Compact Flash, as it turns out, is based on the old parallel IDE standard. So it’s very easy to turn a Compact Flash card into an old-fashioned IDE drive. I messed with an adapter that does just that a couple of years ago. The computer that I may eventually put to use controlling lights on my train layout boots DOS off an old 256MB compact flash card. That’s too small to be useful for taking pictures, but DOS and my 20K program (written in Quick Basic) fit with 240+ MB to spare.

Compact Flash-IDE adapters only cost a few dollars.

SD cards are more common. Not only are most people more likely to have them laying around; you can easily pick up a small one almost anywhere. Well, anywhere that there’s a drug store, a Radio Shack, or a discount store. You can get SD-IDE adapters, but they’re more expensive. And SD cards are slower. That may not matter if you’re putting the device in something older than a Pentium II, but it’s something to keep in mind.

The disadvantages to using digital camera memory as a hard drive are multitasking and virtual memory. They aren’t very good at random writes, so they can get loaded down easily when more than one process is trying to access them. But most people who are looking to put flash memory in a PC that age aren’t looking to build a powerful workstation–they’re building the machine for a specific purpose. Like controlling lights, or playing specific old games that like a specific generation of hardware and operating system.

The upside is that sequential reads are very fast, and flash memory is quiet, cool, and uses very little power.

So it’s possible to get it done inexpensively, without resorting to aged hard drives whose life expectancy may be questionable. And you may be able to repurpose an old card that’s no longer useful to you otherwise in order to do it. Dealextreme.com is a good source for both types of adapters.