#! perl -sw
use strict;

my $term = shift;

my @section;
while( <> ) {
    @section = () if /Header/;
    push @section, $_;
    if( /$term/ ) {
         print for @section;
         print while defined( $_ = <> ) and not /^Header/;
    }
}
__END__
07/02/2011  09:33     1,090,025,317 886391.dat

[ 9:47:22.80] c:\test>junk34 lima 886391.dat >junk.dat

[ 9:48:12.67] c:\test>