Uninstalling 7.1 and 4.7 is easy (Why would anyone want 4.x in XP is beyond me though!), then removing the \Program Files\Netscape directory will remove every last bit of Communicator and it's profile, and 7.1.
Deleting the 7.1 profile is a little more complicated though. First open My Computer, then go into Tools, Folder Options. Enable the viewing of hidden files/folders. Then go into C:\Documents and Settings\
Windows Login-name\Application Data\ - you should see a folder called 'Mozilla', delete that folder and everything in it. Then disable viewing of hidden folders and your 7.1 profile is gone.
Now that they are gone, you can try re-installing 7.1, or you could download Mozilla 1.5 (Just like Netscape), or you could try Mozilla Firebird. I've found that if someone is having problems with Mozilla or Netscape, rather than troubleshooting for ages why the browser won't work, you can just use Firebird and sidestep the issue. You can get Firebird 0.7 (latest version) with the installer from
here. Then you just have to install Flash, Java and all that stuff.
UserAgent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)