It is my opinion that registry.dat should be able to be written to while installation takes place. I suspect that registration data is also stored in this cancerous file. I always change registry.dat to "normal" while I uninstall one version and install another. I then, after registration, change registry.dat back to "read only" to stop its growth.
Some people are under the mistaken impression that the registry.dat growth problem was solved in Netscape 7.0x. This is sadly not the case. Mozilla, I believe, addressed this problem somewhere down the road.
I always recommend Ramona's
Netscape Solutions for her Clean Install and Custom Install instructions.
UserAgent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.4b) Gecko/20030427