The other day we needed to convert a VERY BIG Quark file to work with InDesign. We seemed stumped (and stuck) as InDesign only supports importing Quark 4.0 files or older.
Fortunately, money could solve this problem (I know... that's often the case). A useful recommendation from an Adobe colleague pointed me towards Markzware and Q2ID for the conversion.
The short review... it works! Spending $199 to save having to rekey 250 pages is worth it in my book. Currently it only works with CS1 or CS2.... but you can always convert, then promote the document forward.