Photoshop CS2 Installation Failure in Mac (OS 10.5.8 X Software)

Hi, I just downloaded Photoshop CS2 for my mac. I'm using OS 10.5.8 X software and had some disk repair issues with my disk, so have lost all my adobe design package. Now whenever I attempt to install the new downloaded photoshop, it gives me this message two seconds after entering the serial number (Install Failed: The installer could not install some files in "/ Applications"). And btw I have 60 G out of 149 G available space on my HD, I have created a new admin user account on my macbook and performed the disk repair twice; all these attempts to resolve this issue but nothing seems to work. I would appreciate your support in regards of this matter. Thank you.