CS3 trouble

im trying to install the cs3 trial, but it wont let me, because it says that it is install already, i use to have it, but after the 30 days i thought i unistalled it, then installed my cs2, and now i wanted to reinstall cs3 trial, but when i get to the install part of it, it says that it is already installed. how can i fix this so i can install it again? how do i clean my mac of anything linking the old cs3 files so i can reinstall