I thought InDesign can open XPress files natively.

If you have used certain plug-ins within Quark, like the problem causes pasteboardXT, you will find that InDesign will not open the files. That said, I was under the same cloud as aluminum. I open and convert old Quark files all of the time.

InDesign can only open Quark 3 and 4 files (CS1, I don't know about 2 yet).

If you use Quark 5 you have to save down to 4. I haven't used Quark in long time, but I think if you use version 6 you have to save to version 5, then open up Quark 5 to get to 4. They have special algorithms and such that don't let InDesign or other apps read the files.

On a brighter note, the road ahead looks great for InDesign :)

I've read that InDesign should be able to open Quark 4 files, thanks to some in-built capabilities. I tried, but it didn't work for me. The error message suggested the InDesign may not support the file format, or I may be missing a plug-in that supports the file, or the file may be open in another application. Not in my case.

Have you hear of a Q2ID plug-in by Markzware? It enables you to open Quark 3.3 - 7.x files in CS2 and CS3. It's a great idea – or a 'must' should I say, because the Classic in OSX Leopard (10.5) does not support Classic (or Quark 4 for that matter which only runs in Classic). We at work are about to get it so have no experiences yet, but it sounds very handy and worth the bucks.

Get it here:
http://www.markzware.com/q2id/

I have opened Quark 4 files in InDesign CS2 successfully.

InDesign can open Quark 4 files, but as far as I know it can't open any later versions, which makes it of limited use in that capacity, since I haven't used Quark 4 in awhile now.

There is a nifty trick for Quark users - you can set your InD keyboard shortcuts to Quark shortcuts which makes the transition far easier. It's also helpful if you switch back and forth between the two programs as I do.

The best way to my point of view is to use the plug in Q2ID from Markzware. I use it for one years and I never regret my choice. I think there is a second option, but I'm not pretty sure. Open your Xpress file in the OS 9 system (Classic), save the file in version 4 and come back to OS X to open the file in InDesign. That way need to have the both system available on your hardrive. I found the Q2ID plugin easier to use. All information are saved and usable as it was in Xpress.