It seems as if the latest set of Windows XP updates don't work as well as one would like. I've already run into two time-consuming problems and I'm hoping it won't get worse now that Windows 7 is in manufacturing.
1) The first was an update (don't know which one) that reset many of my internet security settings. The result was that FireFox and IE both stopped downloading files and IE kept saying that my setup was insecure. It took me quite a while, but I finally figured it out: Go to "Control Panel | Internet Options | Internet" and click the "Custom Level" button. What I found was that the options under "Miscellaneous" had been reset to "Disable" instead of "Prompt" as they had been. Once I found and fixed that, I could download files again.
2) The second was the disabling/breaking of scanners. I've had all-in-one printer/faxes for quite some time and use them heavily through PaperPort. All of a sudden, it stopped working: the error message said the scanners weren't setup, even though they previously had been. It wasn't a PaperPort problem as two other machines with the same setup but wihtout PaperPort also couldn't scan documents, even using the vanilla Windows software. No amount of fiddling fixed the problem -- the only thing I could do was completely uninstall the printer/fax software and re-install from scratch. At least that did the trick.
Not a very productive few days, as the problems had to be analyzed, and then 3 machines had to be fixed. I don't scan on my Vista machine, but I'll bet they didn't have a problem.