COMPUTER GAMEs?

hi. my imac is completely out of memory. i want to play some computer games but there is no rooom for them. I bought a 500 Gigabyte external hard drive for my computer. Is there a waay to instal, play, and save my game to this external hard drive so my computer wont need to use any memory but the external hard drive will?? THANK YOU SO MUCH FOR YOUR HELP!!!!!!!!!!!!!!!COMPUTER GAMEs?
yea...but wat would be better is that if you transfer all the stuff u don't use regularly to the external, and then you would have space to put it right on your pc....this way is better, and i am sure that the stuff that takes up your pc memory you don't use every single day, so put all the external stuff on your external hardware and wa laaa....you have space for you games right on your pc................