Find one of those online laptop memory match apps. The online Crucial page should sort you out. I assume you are in the US with newegg, and Crucial are UK based I believe (just checked and they are US too), but assuming you don't have an obscure laptop you can find out the correct memory for your laptop on their website.
http://www.crucial.com/
Just checked and they look to still have the product finder on the main page, plus a new scanner to check your current system.
Cheers
I am 99% probably lying in bed right now... so don't blame me for crappy typing
Current fave quote : "She was like a candle in the wind.... unreliable...."