Is it true that in amseterdam "weed" is legal...I heard it in "harold and kumar escape from guantanamo"?

It's not legal, it's been decriminalised. You can only buy it from the coffeeshops, don't buy it from dealers on the streets, and don't attempt to buy more than a few grammes for personal use. It may seem very relaxed and all over there, but the police are NEVER far away in the Netherlands.