While you're on the Bikesdirect.com website, scoping out the Mercier KiloTT, go ahead and check out all the other bikes on that site.

Another great information site is : Harris Cyclery-West Newton, Massachusetts Bicycle Shop

Articles For Beginning Cyclists
Articles about Fixed Gear Cycling and Equipment
Singlespeed Bicycle Conversions

I highly recommend getting a flip-flop hub so you can run both singlespeed(allows you to coast) and fixed(no coasting). Also get at least a front brake; I have both front and rear brakes.

I'm not sure, but there may be bike shops in NYC that sell used bikes. The guys that work in those shops may be able to help you on what size bike to get. The Kilo will still probably be cheaper, though.