Yep, well....kinda. You can get fizzilla and http://www.mozilla.org. I tried it just today and I was not impressed. It crashed on me in OS 9 and was just generally slow in OS X. The other weird thing was, in OS X, the toolbar is rendered in the regular Aqua style but it looks like they hard-coded the look of the OS 9 style vertical scroll bar - Very Odd.
http://www.mozilla.org/ports/fizzilla - Note that it's definately a work in progress, so it'll obviously have some bugs (and some darn debugging code) but I really haven't had too many problems with it.
Yes, there is a carbon version of Mozilla for OS X. It includes Navigator (which evidently is now known as "Mozilla"), Messenger, Composer, etc. I believe it's available from http://www.mozilla.org; I can't remember exactly where I got it from, but I believe I got it from Mozilla's website.
Having said that, and having used the damned thing for a week or so, I can't even begin to describe how ugly it is. It seems reasonably fast, and not too terribly unstable, but it really looks like it was created by junior high school students. It would look ugly running under gnome or kde; running under the Aqua interface it's just embarrassingly bad. It doesn't even have Mac menus! The menus are contained within windows, à la Windows. It takes no advantage of Aqua; even the scroll bars are really ugly. It seems to do okay with most web pages I've fed it, but it's so hideously ugly, so un-mac-like, so amateurish-looking, that I can't bear to use it.
Mozilla is an Open Source version of what is to be Netscape 6. Pretty much my inderstanding is that Mozilla develops and Netscape takes whatever they like from the OpenSource project and put it into Netscape 6 which will be coming out soon I think (they just released pr 3 for all systems... except OS X). To truly get a usable Netscape, I think you would have to find the distro from a linux disk and port it over, I don't know how but there are plenty of Linux gurus out there that do. I am sorry if any of the above info is wrong, please correct anything I misspoke. Thanks.