Ah yes, good ol' Windows 98 (The best Windows OS in my opinion).
Oh, and I think you've just solved your own problem. I'm guessing that the new Flash Player you've downloaded is only compatible with XP and Vista and that's why the browser crashes every time you want to watch a video. Try reinstalling the previous Flash Player version.
Also, what Flash Player version you have installed now?
PS: Yuna7780 made a thread -
Computer Questions, where everyone can post their computer problems. So if you don't mind could you move your thread there.