awk '/^BEGIN$/,/^END$/ {if($1 !~ /^BEGIN$/ && $1 !~ /^END$/) print}' filename
sed -e '1,/^BEGIN$/d' -e '/^END$/,$d' filename
The sed script has the flaw that there must be at least one line preceding
the BEGIN line.
-- 
   John Pierce	Chemistry, B-032, UCSD, La Jolla,  CA 92093
		jwp at chem.ucsd.edu  jwpierce at ucsd  +1 619 534 0203