A quick Google search did find one reference that said that Netscape Navigator Gold 3.04 would run on Windows 2000, a forerunner of XP. It is probably worth it to install it on Windows XP and see what happens.
Be sure to set a
System Restore point on the Windows XP machine before installing any software! (Some people have claimed that Netscape 4.x has messed up their Windows XP system.) Also backup your original files on the Windows 98 machine before trying anything with them. You may eventually want to ask here about how to transfer files over to the new machine. [I don't think that I used anything earlier than a Netscape 4.0x version, so I would be of limited assistance on that topic.]
You might eventually want to consider "moving up" to Netscape 4.8 (the last version of the original Netscape series) or even to a "modern" browser. I, personally use the Mozilla Suite (which Netscape 6.x and 7.x branched off from) which is currently up to version 1.7.11 (soon to be 1.7.12). The current Netscape, version 8.x, came off of Mozilla Firefox and has no mailing function, although the Mozilla Thunderbird program can provide mailing capabilities.
SillyDog has a complete set of Netscape versions at its
Netscape Browser Archive.
Post back with any more questions. Hopefully someone here can help you, although there are no guarantees.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.11) Gecko/20050728