I know you can install FM09 on more than 1 computer, however if I install it onto a friends computer has anything he does on his file have anything to do with me? i.e will he mess my game up, will he mess steam up?
Well you both wont be able to play on Steam at the same time as only one of you can be logged in at any one time. But if he activates it without Steam it should be ok.
He won't mess up your saved games or anything as they are stored locally on your computer.
Its illegal for 2 people to be using the same license, so no you cant instal it on 2 computers for 2 users, you can however instal it on 2 computers for 1 users eg your laptop and ur pc.