I encountered a similar yet puzzling problem: I just finished an 'internal' WiFi mod to Samsung SWL-2610C on my NetBook Pro with Summit adapter. It worked fine, got the right IP, and connected to Internet. Then, most of the time, I can't connect to the net though it gets correct IP. Soft reset does not help.
It may be due to the driver. Both Rich and I used the same driver successfully on MP900C.