Reformat Question

Forgive me if this has been covered but I did a search and couldn't find it anywhere.

I have a mid-2009 15" MacBook Pro. It originally shipped with 10.5 and I have since upgraded to 10.6 and 10.7. Since purchase, I've moved probably half a dozen times and have lost the original 10.5 OS X disc (and 10.6 which I purchased). As you all know, 10.7 was a download via the Mac App Store.

So, in short, my question is simply this - I'm preparing to sell my MacBook Pro, in order to upgrade, and was curious as to how I can complete a fresh reformat of the hard drive before doing so (remember I don't have the OS X disc that it came with and I've since upgraded twice).

There is 30+ months of possibly private data that I'd like to make sure doesn't get passed along to the next owner.

Also, one last question (somewhat unrelated). I'm not too familiar with TimeMachine, if I were to use that to backup this MacBook can I transfer this backup to a new machine once I purchase one?

Thanks in advance everyone!

- John