Windows 7 & iTunes fail.
This is one of those posts where I hope random Googlers find it and may be able to offer some insight. Alternatively, hopefully I’ll be able to fix this eventually and offer a solution. [While writing this post I discovered it was in fact iTunes that broke my drives. It just adds to the hatred I have of that programme.]
What’s wrong with this picture?

My DVD and CD drives are missing. They used to work fine, but I noticed yesterday that they had vanished. I thought maybe a reset would fix it, but when I turned my PC on this morning, they were still missing. I’m not sure when they stopped working. I keep the old CD-ROM around because it’s excellent for getting a good rip out of scratched CDs with EAC. (It doesn’t cache audio…)
Device Manager showed this:

Opening one of these reveals:

It got me thinking that something had ‘damaged’ the drivers. I thought back and remembered I had installed The Settlers II: 10th Anniversary Edition a week ago, but not gotten around to playing it again. I knew that game used Securerom 7 copy-protection, so I reasoned that maybe it didn’t play nicely in Windows 7, seeing as it’s an XP or Vista-era game. Uninstalling and restarting didn’t fix anything, though that didn’t really mean anything since these copy-protection schemes are notorious for staying on a PC even after the title they’re supposed to be protecting is removed.
I went back to the “Uninstall a program…” dialogue, and had the insight to sort the programmes by the day that they were installed. This revealed that since Settlers, I’d also upgraded iTunes to the much-ballyhooed version 9. Uninstalling that, and all four of its forcibly-installed components also didn’t fix anything.
I started Googling more actively, and came across this blog post of Farhan Ahmed’s where he points toward a fix on Microsoft’s support pages. The fix worked great. The only thing was that it needs to be run in compatibility mode (right-click on the installer file and select “Troubleshoot compatibility”.

This fix is pretty old, so interestingly there have been iTunes issues for some time, not just anything new with version 9. I’m stuck with the programme, for all its headaches, because I cannot find any other way to manage my otherwise mostly-decent iPod Touch.