If creating a new profile for Netscape 7.1 doesn't help then try this:

Open Adobe Reader 5.0 from the Start Programs Adobe Acrobat menu.

Click Edit | Preferences and select Options from the choices in the left panel.

Look under "Web Browser Options". Place a checkmark next to "Display PDF in Browser".
(If it's already checkmarked, UNcheck it, click OK, then go back and REcheck it)

Click OK then close Adobe Reader.
Then open Netscape and try clicking the .pdf file link inside Netscape 7.1 again.
If that doesn't help then close Netscape and search for the nppdf32.dll plugin. All copies should be the same version. RENAME the
nppdf32.dll file inside your C:\Program Files\Netscape\Netscape\Plugins folder, if you see one there, to
Xnppdf32.dll in case the problem is with that copy. Netscape should then use the copy of nppdf32.dll in the C:\Program Files\Adobe\Acrobat 5.0\Reader\Browser folder (assuming plugin scanning is enabled for version 5.0).
Reopen Netscape and try the .pdf link again.
If all else fails you can go back into the Adobe Reader 5.0 preferences, options, and UNcheck "Display PDF in Browser". What that will do is to make Netscape open PDF files using Adobe Reader as a "helper application". Next time you attempt to open a .PDF file, Netscape will ask you what to do with the application/pdf filetype. Tell Netscape to open with the default application.
UserAgent: Mozilla/5.0 (Windows; U; Win95; en-US; rv:1.6) Gecko/20040113