Open Question: Before I install Adobe Photoshop CS4 - How to change the location from C:/ to my external hard drive (D:/)?

Hello, I just bought an external hard drive for my laptop (because my internal is only 30GB) so I want to put all my programs on my External hard drive... ( D:/ ) I am trying to install Adobe Photoshop CS4 - I am at the welcome screen, where it lets me choose a language and what to install. It says "Installation Location C:/Program Files/Adobe" How can I change that to my external drive? (ex. D:/Program Files/Adobe) Please help, I'm just waiting, not knowing what to do... Thanks very much.. :)