Legal and/or philosophical questions...

[Captain Dju]

Hi everyone, here's a couple of silly questions from a Newbie :

I recently got an internet connexion at home and decided to try multiplayer games, so I went to a rental place and rented Battlefield 1942...
As you can imagine, I was more than satisfied (except maybe for the netcode which s**ks ) and decided to buy the game.
I changed the CD key to the one from the game I bought, but I didn't wan't to re-install (heck, who actually LIKES to go through an install process ?), could it be considered illegal to play with a legal CD Key BUT with an "illegal" install

Apart from that, a friend of mine suggested that since he was going on vacation, I could borrow Call of Duty from him and play as long as he's away...
Is that legal

Thanks in advance for answering and my apoligses for my crummy english