A couple of questions
 

I have played Munchkin a couple of times so far and it is awesome, but I have a few questions.

Someone told me that there is a rule that the owner of the game has supreme ruling power when a dispute arises, but I haven't found such a rule anywhere. Is it official?

Some cards state that you must draw cards from either deck (like Duck of Many Things). English is not my primary language so I have difficulty figuring out if that means fx. one Door and one Treasure or one Door or one Treasure?

Re: A couple of questions
 

From the Conflicts Between Cards and Rules box of the Rules:
Of course, this is only if there is a deadlock, and the official rulings provided here by Andrew Hackard and MunchkinMan overrule anything else.

It means you choose only one of the decks.

Re: A couple of questions
 

Only if there's a deadlock and agreement can't be achieved.

"Either" represents a choice in this case, so you may choose from one or the other deck. "Both" would be the word used if you were to take one card from each deck.

Re: A couple of questions
 

Thanks for the quick and helpful answers :)

Re: A couple of questions
 

Unless it's multiple cards, in which case it means "a total of X cards, but you may choose any combination of Doors and Treasures adding up to X."