Is there a way to have 2 different games going on with different protagonists? Let's say a friend wants to play on my computer and I don't want him/her to spoil my character/game. (I once created a new character and all my former character's saved games disappeared.)

Yes u can i'm doing it at the moment all u have to look out for is that u dont rely on the auto- and quick-save since these r 'common saves' other than that there shouldnt be any problems

thanx, i hope it works or i'll have to start all over again

to be on the save side just copy the save file and paste it into another folder if it doesnt go to plan import the saves!