wow. i can't imagine you'd WANT to do this unless you really, really had to. I think you'll find it easier to re-build things in quark than to convert them from .indd files.
whew. that gives me a headache just thinking about it.
have you used any native artwork files in the Indesign files?
have you used any opentype fonts?
have you used any transparency or type or image effects?
basically, a LOT of the things that people use in InDesign don't have Quark 4/5 equivalents, and that's why you're probably better off re-building from "scratch" in Quark.
As long as you aren't using indesign CS or CS2 (which you probably are), and as long as you're not trying to go to Quark 6 (which you probably are, also), then I guess it's possible that if you've got very, very basic designs that use only type 1 fonts and .tif/.eps links with no special indesign-only properties, you might be able to get it to work.
Can you be more detailed about your problem?