awk -F - '"2011/03/25" < $1 && $1 <= "2011/04/04"' filename
ou, se as datas forem mais dinâmicas
d1="2011/03/25" # or whatever commands to set this date
d2="2011/04/04" # or whatever commands to set this date
awk -v start=$d1 -v end=$d2 -F - 'start < $1 && $1 <= end' filename