I have the same problem. The issue is really the fact that Nintendo's Wifi adapter is horribly unreliable. After I get a connection, it's fine, but when my wii is 3 feet away, I should NOT have trouble with it. There are no other wireless devices installed in my area, aside from the wiimote itself.
Luckily I didn't buy that disgrace of a product, as a friend of mine already had one. I'll be buying the USB Lan Adapater that DATEL that has already released. Not going to wait on nintendo's "we'll get around to it" attitude.