Lost Mac DVD, how can I recover?
Unfortunately I lost my OS X cd and for some reasons I need to reinstall the operating system.
How to reinstall a Mac if I don't have the installation cd?
You'll need to acquire a Mac OS X install DVD, I'm afraid. If anyone you know has a copy you could borrow it; alternatively a Snow Leopard install DVD is only £26 (Sterling) from Apple. Alternatively, I believe AppleCare will replace your system restore DVD, but there's a cost, and I don't know how large it is.
Be careful when using another Mac's system restore DVD, though - they often contain hardware-specific drivers. At the very least, make sure that the Mac you borrow the restore DVD from is at least as new as yours. Ideally, borrow from one with exactly the same model.