I've been trying to install  on a shared host, but have been running into problems. I had everything set to 0755 but got a 500 error until I changed the permission on the idex.php to 644 and then things started to work. That doesn't make sense to me, but...
I've been able to access the wiki but when I try to login I get

Fatal error: Non-static method _PearDbPassUser::_PearDbPassUser() cannot be called statically, assuming $this from incompatible context in /home1/..../wiki/lib/WikiUserNew.php on line 1118

Clearly this is indicative of a deeper problem in my installation, but what?

You can see the behavior at http://physandmath.org/wiki i haven't set any restrictions as yet.