I am not well versed in the more esosteric principles of null modem cables but you could try using a PhoneNET box. There's only two wires...if you could find out what wires are critical, then it could be just a cake walk.

Why? Simple -- if you saw the LocalTalk section of the Guide, I have there an RJ-11 tool and some RJ-11 jacks. All you'd need then is either RJ11 cable to your DE-9 port or run the DE-9 cable to the RJ-11 jack.

I don't know how many people have that kind of tool these days though.

Have you seen this post?

I would say I would like to know how to transfer files via OS X with a serial USB method. Apparently you only need two pins, so yeah.

Actually now that I think about it, a MacMasterNullModemCableHack™ would be nice: you'd have one end with USB, mini-DIN-8 and DE-9, and the other with DE-9 and mini-DIN-8 connectors. Then you could link just about anything together. USB serial data transfer to a 512K? Sounds good to me.

At any rate, once the hardware is set up right, assuming it is set up right, the rest is all wrangling with software.

EDIT: If you do get such a neat setup going, then I could be easily coaxed into adding an entire new section to the Guide: Serial Data Transfer. I'll have to work out details since I like plenty of details and easy to follow steps (unlike Linux ;D "Just install via the repos, configure and you're done" yeah right*) so I'd have to demonstrate OS X, Classic OS, Linux and I'll probably just demo Windows XP.

(*: Not that my Guide is particularly easy to follow, but...)