How do I install an older version of Safari?

Awhile back, more than a month, I clicked a link on Facebook that caused Safari to stop working. I can't remember the exact details but I believe I got a message saying that Safari has stopped working. So I eventually downloaded and installed a newer version of it which then proved to be incompatible with my operating system, OS 10.7.5 which is the most recent OS that my computer is capable of. So now I can't uninstall or modify the exiting Safari installation because the OS needs it. I have an older OS on another hard drive which has Safari 4.0.5 and I'm able to use that one but I would prefer to get Safari fixed on my main OS. Anyone know how?

Thank you,

Jon