Well, that is quite odd!

Do you have zonealarm or something similar running on your PC that might be blocking DNS services to PING or PingPlotter?

If you try pinging to "66.218.71.84", what do you get? This is what www.yahoo.com resolves to for me.

Can you try other hosts? Does www.pingplotter.com, or www.winfiles.com behave anyh differently?