Fatal browser / internet connectivity problem

Sorry this is way long, but I might as well be thorough.

Something rotten is going on with my os 10.5.8 MacPro desktop in regards to connecting to the Internet and I need help figuring it out. I really don't want to wipe my HD and reinstall e v e r y t h i n g - if possible - because its only internet connectivity thats a problem.

Safari started intermittently stalling while browsing/downloading/uploading about 2 weeks ago. I could relaunch and it would work again. Or reset my modem and it would work again.

My other browsers have been broken for a long time. Firefox I gave up on long ago because it would just say "Stopped" in the status bar and would quit loading pages. Internet Explorer basically opens with a working freeze and has to be force quit. And Chrome also simply does not load any pages period, just launches with a blank page and refuses to load any page. Obviously, these are symptoms of something wrong but I've been busy and Safari worked fine. I don't know if might have picked up a virus? It would be a first in 20 Mac years, so I don't own any anti-virus software... make of that what you will, I'm on a Mac.So I've been using Safari exclusively without a problem - until these recent freezes.

Resetting/emptying cache/deleting cookies didn't work. My DSL provider proved that my modem and internet connection is fine - mail and ftp still work fine. Pulling out Internet Plugins didn't help. Finally I decided to delete and re-install Safari. I dl'ed the latest Safari for my 10.5.8 system (Safari 5.0.6) from Apple, then methodically deleted all Safari support files from Applications, Library & Preferences according to uninstall info I Googled. Then I ran the 5.0.6 Installer and the process went through smoothly and asked for restart. After restart, there are no Safari files on my computer. I did a search - nothing! None! I restarted. Nothing. I re-installed it again. Same thing - appears to install perfectly, but no files on my computer. I thought maybe its installed onto an external drive. No. It didnt.

I ran Disk Utility - no problems. Theres no router, no firewall, no filters, DSL straight from the wire. My computer has only one Identity - Administrator. AT&T Internet tech support found nothing wrong with my connection and suggested I use their house subscription tech support service. So I signed up and next day spent an hour on the phone to Mumbai, trying Network Utility things and more, before the guy gave up and suggested I call Apple. He was surprised to hear that costs $90, last I remember.

Now I can't use the internet at home at all. I'm writing this from work. What gives? Any ideas?