I had something similar with a Netgear at work. A couple of good pings and then a sequence of dropped packets. Other PCs and equipment worked fine. I solved the issue by manually lowering the MTU of my Mac to 1280. You can find the settings for the MTU in the network system preferences. Click on your wifi adapter and then open the Advanced properties. The MTU option is under the "hardware" tab. If it doesn't work, I suggest that you go back to the default (automatic) setting which is 1500.