while ( my ($key,$string) = each %oldhash ) {
   my @elements = split /\s+/, $string;
   $newhash{$key} = \@elements;
}

# You can now access data from it like this:

# print the first element in the array referred to by $key
print $newhash{$key}->[0], "\n"; 
# print out all of the elements for a given key
print "$key: ", join @{$newhash{$key}}, '-', "\n";