As is usual for software companies, Quark’s stated position on old software running under new operating systems is: “It’ll probably work, but we don’t support it.”
Here’s a statement from Quark that I found in their online forum:
If you are planning to upgrade to Snow Leopard (aka Mac OS X 10.6) or Windows 7:
Make sure you install/update QuarkXPress 7 to the latest version (7.5).
Though we do not foresee any issues why QuarkXPress 7 shouldn’t run under these operating systems, Quark will not officially support QuarkXPress 7 under Mac OS X 10.6 or Windows 7.
If you want official support, please stay with your currently supported operating system (QuarkXPress 7 is officially supported under OS X 10.4 & 10.5 and Windows XP & Vista) or consider upgrading to QuarkXPress 8.
QuarkXPress 8 is officially supported under Mac OS X 10.6 & 10.5 & 10.4 as well as Windows 7 & Vista & XP.