Upgrade iMac 8.1

Have to admit I am not familiar with this machine. (or any of the Intel Macs)
I was given an iMac 8.1 running OSX 10.5.8
The owner had a 10.6 upgrade DVD but when I try to run it to upgrade, I get a message "will not run on this version."
Actually, what I really need to do is just upgrade the browser.
Safari 5 connects to very few websites...I can't even connect to the Apple store
Any idea where I can get a browser that is better than what I have>
new version of Firefox will not run
Also:
I wanted to empty SOME files from the trash bin NOT all of them
The ONLY option is to empty the bin>
I did Google and found two answers
Either hit the command or else the option key
That gives no option to delete only that file
Thanks