Mac OS X & PC Windows 7 64bit Home Premium Wireless Network Speed Slow

I have a 24″ iMac (wireless N), and a Sony F Series Laptop also with wireless N. Router is an Apple Airport Extreme N. I have them networked wirelessly and that works fine, however the transfer speed between them is terrible, averaging 2mbps max. Transferring even small amounts of data is a chore, I am waiting right now for a 27GB transfer which is slated to take 3 hours. Independently their speed is fine (i.e. connecting to the internet, downloading).

Why is this so slow? Is there anything I can do to improve the speed?