Note that most of these solutions (all of them?) will stop once one of the files runs out - if one file is longer than the other, the excess will be lost. Though, it is really trivial to append whatever's left after the join:

# join files in whatever way you feel like

if (not eof(F1)) {
  print <F1>;
} elsif (not eof(F2)) {
  print <F2>;
}
[download]

-- Dan