The male-female "extension" cables would certainly need to be straight through, but I would also expect the male-to-male cables to be straight through unless specifically labeled as crossover cables. I got my serial cable at Radio Shack, but I got mine probably around 1993 or 1994 and I could hardly find anything that even had serial connectors on it at Radio Shack's web site this morning. I suspect that this cable would work (the laplink reference is probably to the old Laplink software, which I think could work with straight-through serial connections - it's been at least a decade since I used Laplink, though).

EDIT: there are also some options here , but going through them makes me want to go home and dig out the serial cable that I know I've used successfully. I'll take a look at it this evening.