Well after messing around with various files, it might not be that good of info. Depending on how much time and effort you want to put into locking the prefs - it involved editing the .XUL files (similar to editing html) which are packaged in different .JAR files located in the chrome subdirectory under Netscape. After they're extracted you can remark the corresponding command lines in the NetscapeOverlay.xul file (by using <!-- at the beginning and --> at the end of the command line), re-package the .JAR file and the Preferences pulldown will be completely removed from the pulldown.
After doing that, I wanted to further 'customize' the Netscape 7 install and I found that there are a LOT of different .XUL files that could be modified to tweak NS7. So I guess the good part was that I had found info, but that it was WAY more difficult to hide NS7 prefs than 4.7x....