Shouldbe pretty simple getting one to connect to the other. Make sure AppleTalk is active in both Mac's Chooser. Double-check that both have the correct network connection selected. If sharing is turned on with one, it should then show up in the other's Chooser. Since we're just doing plain ol' LocalTalk updating clients shouldn't matter. That's only important if we need to talk to much newer Macs, or get on the WWW. Correct me if I'm wrong on anything, of course...

That's the best advice I've got to start with before we get real geeky.

EDIT: What system versions do you have on the 540c and Classic II?