Well, I've installed 7.5.5 and things are looking good, except for one thing: I can't connect to the internet. "Error -23009", insufficient resources, which sounds to me like a router issue... except that when I run OS 7.6 (zip 100 boot disk, so apparently that works), I don't get any error at all. Fantastic.

So! Has anyone got any ideas? I'm going to try to dig up a walkthrough that might cover this, since those are usually idiot proof. Worst case scenario, I restore my previous 7.6 system from backup, install 7.5.5 on the zip disk and use that to support the Apple IIe card. But that sounds pretty complicated. :-/