My Mac REALLY hates RTFs: any app (including Finder) hangs

Question

This problem is affecting my work Mac, a mirror-drive-door 1.25 GHz G4 with 768 MB of RAM, running OS X 10.3.9.
A couple of days ago, it became deathly afraid of RTF files... or so it would seem, since any time an RTF is anywhere in sight, the application that's trying to access it, including the Finder, will hang.
Some recent examples:
Entourage: Trying to read an email from a coworker that contains an RTF attachment, just reading the MESSAGE, not opening the attachment, hangs Entourage.
Finder: Hangs just getting a directory listing if there's an RTF in the directory. If there's an RTF on the Desktop, Finder just hangs, period.
TextEdit: I was writing a document, and when I came to save it, as soon as it was saved (as an RTF of course), TextEdit hung.
Downloading a new utility, opening the DMG file, which contained an RTF, again hung the Finder.
I've tried deleting any com.apple.* preferences that were modified in the last week and rebooting, no luck. The only way I can get around this problem is to go into the directory via command line in Terminal and delete the RTF file. (OK, that's ONE thing that doesn't seem to be affected by RTFs, but that's it.)
It's not any one particular RTF file; as the examples demonstrate, ANY RTF, including one I've just created, will do it.
I'm no novice with the Mac; I've been using Macs exclusively for 14 years, and I work as a web developer. In other words, I'm a "power user" who's spent 8+ hours in front of a Mac almost every day for a decade and I know the system extremely well. I've never seen anything even remotely like this.

Answer 1

OK, here's an update: I just created a new user account on this computer and with that account I am able to load RTFs OK. So it does seem to be some kind of preferences issue, or at least something specific to my main user account. I'm still stuck on exactly what it could be, though.