from sr20forum:

you will need a manual crossmember all the trans mounts, brackets, cable, shift rods, shifter, knob speed sensor crank sensor/flywheel sensor (on a b14 only) you would need to make the crank sensor wire longer if it is automatic since the sensors location on a manual is more towards the front as opposed to an auto which sits higher, you would need to rewire your reverse lights into the manual harness and the nuetral safety switch. the clutch pedal and bracket you would need a new brake pedal also, drilol thru your firewall to get the cable to the pedal and misc and most important the transmission.
there are alot more little misc parts i did not list because i dont remember what they were.

this guy also suggested selling the auto, and buying a new car.