I find this chart handy for AFP compatibility: http://www.applefool.com/se30/#afpnetwork

32-bit addressing is disabled by default on my 68k Macs running 7.5.x, so it turns off every time the PRAM is reset-- which is very often with no battery installed. I usually think it's on until I run out of memory or notice the System is "using" 65MB instead of the 6MB or so it should be.