Well, Quartus just wasted my Saturday, but creating a brand new VM, installing a fresh copy of XP, updating everything to the latest patch-levels, and doing a re-install of the 11.0 software seemed to do the trick...
Silly me, because of Parallels, for a little while there I'd forgotten I was running Windows (and don't tell me to use Win-7. That crashes on shut-down on three different machines). If Quartus can run on linux, why can't it be OSX-native ? Come on guys, you're only down the road from Cupertino... Pop over and talk about it...
Simon