OS X installation problem

I have replaced the hard drive of my Macbook (white), from 60GB to 120GB, coz my original drive cannot be detected so i have to replace it.

Now this is my problem: i don't have the recovery cd bundled with my macbook. How will i install mac OS in my macbook? Need it badly, please help me....

if you ring apple i've heard they are able to supply you with them for a small charge.