quick network question

Hi All, this may seem like i’m being lazy asking this question but i am struggling with this. We have 2 domain names, marsclub.org and nypower.org both currently pointing to 2 different sites. The hope is that nypower.org could just be pointed at marsclub.org/nypower but still remain nypower.org. it would not matter to us, if clicking on a link we change the url.
Before i get to much deeper can this even be done??