1800 feet is distance from the WAP to the wireless client, not radius or diameter, although it effectively is the radius.
That's outside ... with absolutely no barriers, and void of atmospheric conditions. Even with one wall between the WAP and the client the distance is easily cut in half.
I'd expect a MAXIMUM USABLE range of 300 feet. If you knock the speed down to a maximum rate of 1 or 2 MBs then the signal to noise ratio will drop because it's sending the data slowly and makes sure the packets get there. It's more about packet loss than anything else... if there's little packet loss then the connection will go farther and be more stable, but not that much more stable or further!
Your best bet will be 500 feet at under 1 MB per second stable.
With 802.11a then the speed will octuple and the range will double.
[EDIT] You're not going to successful, or satisfactorally, set it up with only one WAP... but go buy a WAP from BestBuy, you can return it within 30 days no questions asked (but verify that BEFORE you buy it).