For info, I have the same problem with my wife's netbook (Asus Eee PC running Win XP Home). We have Word 2000 and have used this for years without issue until the latest Avast definition update.
I can't find a way of excluding Word from on-demand checking (and not sure I'd want to anyway, since Word macros are a major malware vector). So, for the time being, I've switched my wife to Open Office as that can do just about everything she needs Word for anyway. I've reported the false positive, so hopefully Avast will resolve the issue. In the meantime, we'll just have to continue using Open Office or switch to another AV solution.