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Did you ever solve this? I'm very experienced and I'm finding the same thing.
You don't specify exactly which directories need to be write permission. I wouldn't normally make a few hundred files/folder write permission since one is asking for trouble, but I have done so.
The install page returns when I unset permissions so therefore I assume there is something that needs to execute on 1.php, and it can't do so. Only the top level folder needs to have write permission for it to not work.
The error log says "[08-Feb-2010 17:15:10] PHP Warning: Module 'ionCube Loader' already loaded in Unknown on line 0"