I'm hoping to put this combo in here and wasn't worried until I read this, I think as long as you don't work directly off the server you'd be fine.
As Erik says, all the probs seem to be trying to run quark on Leopard workstations, I don't think its even worth trying v6.5 on Leopard, certainly Quark are not going to work on making it compatible. I'd try with quark7.31, make your decisions and maybe take advantage of the free upgrade to quark8. Snow Leopard may well be here before it's bug free.
If it makes you feel any better I've currently got Tiger Panther and OS9 workstations all talking to PCMacLan running on a WindowsNT Server and although its really hopeless and slow it doesn't have probs opening and saving quark files over the network (not that I ever do that of course
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... there was the puzzle of why the sun came out during the day, instead of at night when the light would come in useful.
Terry Pratchet