You can do a simple search to see if the N number you want is already in use here:
http://registry.faa.gov/aircraftinqu...um_inquiry.asp
You will see a couple of different status' for the n numbers: assigned, unassigned, reserved, on hold, and assigned but questionable. The two to work on are the un assigned which means you can apply for them now, Just send the info to the regiistry w $10. The odd thing in the whole system is the "on hold" status. If a plane crashes or something else odd happens they put the number in this status so that the grieving family doesn't see the N Number flying again the next day.


You can also search a range of numbers but it is an ackward search function.
http://registry.faa.gov/aircraftinqu...av_inquiry.asp

HTH If you need any help with the process email me. I work right across the street from the registry.