Changing from copy to real version of Leopard

Hi there,

I am wanting to upgrade to Leopard, but because of several complaints about various aspects to Leopard I am reluctant to buy it right away, so I am thinking of giving it a try through torrents (I know).

But I want to know if I got that route can I:
A) Use my restore CD (10.4.xx) to go back to my original OS X?
B) If I like Leopard and buy a legit copy can I install the real one over the one from torrents?

In any defense I bought my MacBook shortly before Leopard was released and qualified for the 10 dollar upgrade, but since it was bought in Hong Kong, America Apple wouldn't offer the same upgrade package for 10 dollars. I do not believe in pirated software, I do believe in trial though. Thanks for your help.