I'm so sorry you're all having trouble with NS4.x here... if I had my druthers, I'd like to have it work too!
But Opera 5 is cool, handles the board very well and doesn't interfere with NS4.76 or anything else at all... in fact I almost always have both running at the same time now.
You could give that a try... I believe you can get it for 30 free (no ad banners) and after that you can keep it for free with ad banners or pay the fee and get rid of them, which is what I did. I don't regret it...

But if you want to go the banner route you can at least in the preferences specify what you'd like to see, so you aren't bombarded with stuff that doesn't interest you.
I'm finding that unfortunately for Classic MacOS the options for browsers are dwindling... most every, especially the free ones are OS X only, which is something I'm just not ready for. I too was NOT going to put IE on the machine!