[marcmac]

++ nvram -p
++ awk '/^ram-size/ {print $2}'
+ memhex=-2147483648
++ printf %d -2147483648
+ mem=-2147483648
++ expr -2147483648 / 1024
+ memkb=-2097152

That's very strange - on every other mac I've tried, I get a positive hex value here - you've returned a negative integer.

Edit this script, and replace
mem=`printf "%d" $memhex`
with
mem=2147483647

THen rerun zmmycnf and start mysql again...