Hi, Tom --
You need to have both Courier and Helvetica fonts active for XPress to launch. Because Classic does not see .dfonts that are active in OS X, you'll have to activate Type 1 or TrueType versions of these fonts, if you haven't already. Take a peek in your OS 9 System Folder > Fonts folder -- are they in there?
If they are, the next thing I'd do is move your XTensions and XTensions (Disabled) folders to the desktop -- do not delete them -- and try launching XPress without them. If XPress launches, you have an XT conflict in one of those folders (and yes, even though they are Disabled, XTs in that folder can still cause problems because XPress scans that folder at launch).
If that doesn't work, try moving your XPress Preferences to the Desktop and restart XPress, allowing it to build a new Preferences file. If that works, it means your old Prefs file had become corrupted.
Let us know if any of this helps.
peace,
Linda :) <born and raised in Iowa!>