yeah by far the easiest is just take the harddisk and put it in a ide usb dongle(10$-30$ bucks).
second easiest is to get INTERNET on the machine. it's not that hard or impossible, then just ftp the files over. you need to find a isa network card though. ebay should have plenty of them. also this is the best way if you intend to play some old games or what have you with it.
third easiest, to get a null modem is also doable, the newer machine can use a usb serial dongle. if you don't find a null modem cable it's easy enough to make one from a serial cable. then use some program to transfer the files over that. it's just 20 megs so speed isn't a real problem.
then there's possibilities of using some crap like ooold zipdrives etc. possibly a cdr drive as well but eh good luck with burning on that machine..