Your User Agent seems to be changing with each of your posts. Are you just playing with your system?
One of our regular responders here has had no success in trying to install Netscape 4 on XP. On the other hand, someone else was able to make it work. I haven't attempted it.
Why are you trying to use an obsolete application?
To clear the name from the Add/Remove list, see [sdp=95253]this[/sdp] post.
If you have multiple versions of Netscape installed it is possible that there are incompatible files all mixed up in commonly-named folders. (I always do Custom installations and give each product its own folder tree.)
Then just Delete the program folder tree if you can identify the proper one.
You'll have to examine the Registry (both HKLM and HKCU), under Software\Netscape, and select the applicable keys to delete.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:220.127.116.11) Gecko/2009011913 Firefox/3.0.6