as this seems to be a reoccuring topic:
Mac OS X
The first version that supports Mac OS X 10.5 (Leopard) is QuarkXPress 7.31.
The first version that supports Mac OS X 10.6 (Snow Leopard) is QuarkXPress 8.1.
The first version that supports Mac OS X 10.7 (Lion) is QuarkXPress 9.1.
Mac OS X 10.7 (Lion)
Please note that Lion doesn't support Rosetta anymore, so that means that any non-MacIntel-native applications won't work. So QuarkXPress 6.52 (and before) will not run on Lion, you either need to stay on previous versions of OS X or might have to consider upgrading to QuarkXPress 9.
Mac OS X 10.4 (Tiger)
Please note that QuarkXPress 8.5 is the last version of QuarkXPress that supports OS X 10.4.
Power-PC based Macs
Please note that QuarkXPress 8.5 is the last version of QuarkXPress that supports PowerPC-based Macs.
The first version that supports Windows Vista is QuarkXPress 7.3.
QuarkXPress 7.31 (and higher) is certified on Windows Vista.
The first version that supports Windows 7 is QuarkXPress 8.12.
QuarkXPress 8.12 (and higher) is certified on Windows 7.
All lower versions of QuarkXPress (e.g. 7.2, 7.01, 6.52, 5.01 etc.) are not supported on Leopard, Snow Leopard, Lion, Vista or Windows 7. "Not supported" means it may run but Quark didn't test it and doesn't offer technical support to make these combinations run. If you need help from Quark's free technical support, you need to run a supported platform.
MatthiasP.S.: Info about QuarkXPress 8 & 9 & 10 here: http://forums.quark.com/t/21811.aspx
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