In the US, one can request that the university from which one graduated to send copies of one's transcript to other universities (graduate admissions) or prospective employers. I would like to know what is the provision in the Netherlands, if one needs to send a copy of one's transcript to the university in the US.
The best thing to do is probably to contact the student administration of your university. They can make certified copies of your diploma (and presumably also grade transcripts, etc.). You can also contact the Dienst Uitvoering Onderwijs at http://www.duo.nl/, which are also authorised to make certified copies.
However, it may be that "ordinary" photocopies suffice, if you tell them that you can show the originals later if necessary. You would have to check with the admissions office though, I do not know about the situation in the US.