Software :: Safari Won't Work - Can't Reinstall Because "This System Cannot Use This Software"

I have a Mac OS X 10.3.9, processor 450 MHz Power PC G4. I tried downloading a new version of Safari not really knowing if it would be compatible with my computer. I wanted to see if I could update it because I had been having a lot of issues with pages properly loading. I've been using this mac for 4 years, it was not mine to begin with, so I have no idea what applications have been downloaded or what. Once I downloaded the new Safari and restarted my computer, I couldn't open Safari anymore at all. Now I've deleted the Safari icon from Finder in hopes of reinstalling it again. I have no disks what so ever pertaining to this mac.

I am working on Internet Explorer, but this browser does not work well with my mac at all. I need my old Safari back. I tried redownloading it, but everytime I do I get stuck when I try to install it onto the cube hd. It says "You cannot install this software on this volume. This system cannot use this software." Plus I don't have very much space on my cube hd. I don't know what to do? How can I free up space AND get my Safari browser back??? I'm very much a beginner at this so I don't really know all the technical terms that I've been reading on the internet for the last 5 hours. I've been searching the internet desperately and I can't find an answer. Btw, I'm a college student borrowing this computer from my stepdad so I only have the computer, no disks.