So, I don't know if you tried to install 4.03 in the location of another Netscape, but the way I did it I was able to remove it. But, I think that I answered your question. 4.03 will not work.
P.S: I remove 4.03, but when I tried 4.8, it acted as if 4.03 had possessed it., in spite of the fact that I had used a different folder for 4.03. So, I had to remove 4.8, and tried to reinstall it. And, when I went to reinstall, it could not do it, because, allegedly, communicator was running. not sure where, but normalcy was restored for a minute after that. I tried to use 4.8 to post, but I could not enter more than one line.
Actually 4.8 is pretty decent. And, don't forget that Users folder is hiding like the NS7.x is hiding its Profiles. Learning something every day!
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.3) Gecko/20040910