Hello zee2007,
Assuming that you entered US as a non-immigrant and were never out of status, you have nothing to worry about. Simply request the Status Information letter which usually arrives in 4-6 weeks (you can also speed up by calling, but I am not sure if it really does). Go to the following thread (which is a Sticky) for more details:
http://boards.immigrationportal.com/showthread.php?t=197782
and look at the Exahustive post by JohnnyCash (Post #6). You will find that:
Letter from Selective Service: If you are a male who is or was previously
required to register with selective service, then you must bring a "Status Information Letter" with you to the interview, which you can easily obtain thru Selective Service. No need to explain to Selective Service why did you fail to register if you did not register with them before. Because they don’t care about its reasoning as they could only give you a latter that would only explain whether you were required to register or not. That is.
Your application for naturalization will be denied if you are a male and were in the United States between the ages of 18-26 and failed to register for selective service willfully and intentionally. But if you can convince INS officer that your failure was not willful then officer will be able to approve your application. So, it is better to bring an explanation letter (a notarized affidavit) with you at the interview, wherein you should explain very clearly that-[1] your failure was not willful; and [2] you were not aware of this obligation; and [3] you did not receive any notification on this either from USCIS or from Selective service.
However, you should know that if you were in the United States between the ages of 18-26 under any status, even as an illegal, then you were required to register for selective service.
The only exception to it- those men who were here on valid nonimmigrant visa. Men's age does play a very important role during the time of naturalization. Because if a male did not register with Selective Service when he was required to register, no matter for whatever reason, then officer may deny his application unless he reaches 31 of age. Once a male reaches to the age of 31, then 97% of times this issue becomes irrelevant. And after the age of 37, it is 100% irrelevant because then this Selective Service issue becomes completely mute and a non-issue even though a person had failed to register deliberately. For more information, read the info here-
http://www.sss.gov/must.htm
http://www.sss.gov/FSwho.htm