yes you will need more than just a remote more than likely too if it is an 03 since it wasnt standard on the EX until 04. it was an option in 03 but if you dont have the little black keyless box under the dash near the steering column then a remote will do no good.
I have an 03 ex. For about 100 bucks I bought a kit from H and A. All it is is two key fobs and a small black box that plugs right in under the dash. I followed the directions and it took about 10 minutes to install and program.
Press the lock button once: All the doors lock and the lights flash.
Press the lock button a second time: The horn sounds.
Press the unlock button once: The driver's door unlocks and the lights flash. (If you open the door immediately, the dashboard will beep as the lights flash.)
Press the unlock button a second time: The other doors unlock and the lights flash.