I'm have a System 7.0 Macintosh with MacTCP. Never tried ping on Macintosh itself, but the browsing the "internet" works fine.. I have even used MacTCP on a Plus with a serial cable and System 6.0.8 (as described here)

I forgot what to choose on System 7.0 at the moment, but you need ethernet drivers for your card, choose Ethernet (in MacPPP? Or Chooser?), then set MacTCP up with your ip.. I also selected something in the Chooser, but honestly forgot what.