Windows Remote Desktop

Ok, my parents are soon going to be getting rid of their old pc and my old pc and my gf's family is getting rid of thier old pc. While i dont have a use for all of these systems, i think i might mix and match some parts to get a decent machine that i can use strictly for the windows only apps that i get here at school occasionally.

anyways i stumbled upon Windwos Remote Desktop which is very interesting indeed. Now i dont have the pcs yet and i dont really have all that much room. What exactly does this program allow me to do?? does this mean that i can basically run the windows programs and computer through my mac? or what? the microsoft sight seems to be vauge on details