Last time I saw something like that was with Windows XP, but it affected ALL the text in dialogs, so this is not the same (fortunately for you -- I eventually had to wipe and reinstall the OS on that machine). I used to see it on Macs running System 9 with Suitcase, and it meant it was time to rebuild the Suitcase database.
In this case, I'd try trashing the prefs as the first step. See Replace Your Preferences
Good shout, that has sorted it.
Thanks for the help!
All the best,