This procedure removes the splash screen from Netscape Communicator 4.5 and 4.7. It may also work with other versions, but it's only been tested on version 4.5 and 4.7. You will need a hex editor, such as UltraEdit-32 from IDM Computer Solutions. (They have not endorsed this, BTW!)
Do this at your own risk!
If you screw up, I'm only going to laugh at you.
What this does is to replace the entry for the splash dialog box (resource ID 490) in Netscape's resource table with another non-existant resource ID (472). So when Netscape comes looking for the splash dialog box, it can't find it, gives up, and goes on its merry way. You will still see the "Loading preferences" message briefly while Netscape loads in future, but it's not nearly as obstructive as that great big stupid splash screen.
Note: My first attempt apparently caused Netscape Messenger to do weird things. The hack you are looking at now is the corrected one which doesn't do weird things.
Splash screens when poorly implemented are obnoxious, self-indulgent and annoying. Netscape's monstrosity is a perfect example. Netscape can take a while to load, especially on slower computers, so it is often convenient to let it load in the background while continuing with other jobs. But then up comes the splash screen, big enough to get in the way of everything you are working on, right in the middle of it all. To make matters worse, it forces itself above all other windows so that you can't even see to work on another application, and you're forced to stop everything until it goes away. If you're a developer, be strong and resist the urge to add a splash screen. If you can't, and no amount of therapy helps, then at least provide an option to switch it off!