I work with Joe Sixpacks all day. Maybe I can clear up some misconceptions.
wv] Joe Sixpack should not need to know how the internals of his computer work, just the basics.
I'm about to break your heart...
wv] I do expect Joe Sixpack to know about Windows and preferably the existence of alternatives
What alternatives? Joe only knows Windows. He might have HEARD of Macs, but he has never before seen these mythical machines.
wv] about a hard disk and what it does and how big he should want it
Joe has no idea what a hard drive is, let alone how big he should want it.
wv] what a processor speed roughly means
Such topics are beyond the ken of Joe.
wv] and whether he would need 1GB or 2GB or 4GB of memory for his needs.
Joe doesn't know the difference between hard drives and memory, never mind how much memory he might want to have
More importantly, for all these gaps in his knowledge, Joe doesn't care. He doesn't WANT to learn. He may pretend to listen if you try and explain, but if you quiz him on it you will find he hasn't really been paying attention, no matter how simply or how many times you explain it.
You know what Joe does know? He knows the Power button, and he knows what to double click for teh pron. That's all Joe knows, and that's all Joe wants to know.