Wired speed: excellent -- Wireless speed: like an 80s modem (tops).

I just purchased a new Netgear RangeNax NEXT Wireless-N router (model
is WNR834B) but I have already spent about 8 hours attempting to get a
decent wireless connection out of it.

When connecting to the router wired I get an excellent connection speed
but when I try to connect wireless, the speed is incredibly slow,
almost non-existent, even though I'm getting an excellent signal. When
connected, it sometimes says that the speed is over 240Mbps but that is
obviously not true.

I already ruled out my wireless adapter being the cause of this because
I can connect to other wireless networks perfectly. I also tried moving
the router to different locations inside my apartment but none have
made any difference. I tried changing to several different channels and
nothing.

Pinging the router gives me speeds <1 when connected wired and between
2 and 2000 ms when connected wireless averaging about 15 to 30% packet
loss.

I'm running out of ideas here. Is there something I could do, something
I could be missing? Please let me know of any useful information you
might need from me to determine the proper solution to my problem.
Thank you.