Ethernet on a 5xx is not RJ45, it's AAUI. As for wifi, the ioexerts driver is for OS X only; drivers for classic are free, and you'll need the rev c PCMCIA expansion box (goes in one of the battery bays) which is incredibly hard to find. In 8MB RAM I wouldn't dare run anything higher than 7.1.1p, I'd at least double it before putting on 7.5 or higher, if you want any speed that is. 7.1.1p has mactcp (which is fine unless you "need" DHCP). Serial network links are only possible if you have another mac running as gateway.