I've put up 4 tiny pages that show the differences between how NS and IE display fonts when using CSS. Even the main Sitepoint page displays slightly differently (verdana font is slightly smaller in NS).
Of course, <font size="1"> displays exactly the same in both browsers but CSS px & pt do not (depending on the size).
I have Netscape 4.73 and the Communicator version is 4.03 on mine. Weird, I never noticed that. Anyway, I have to agree with you: it is a pain how all the different browsers display stuff differently, like fonts. One thing that helps is if you make the font size 10pt it will be readable on all platforms. I don't normally use anything smaller than that size.