What else to do for prevention?

Well due to a power supply problem I could not use our main computer for a couple of weeks, now is up and running... But, other that need some more RAM I Am thinking in doing some kind of back-up from the old computer that we used for awhile to our main and I know of the direct cable connection way, my question: which kind of cable do I have to use for this? the 9 pins straight through (female-female) or the Null Modem cable in any case is there another way to do this? And of course, what is the procedure? My main computer is 1.6 Mhz. running XpPRO and the other one is a 366 Mhz. running WIN98SE, recomendations are welcome!!!