Unfortunately Symantec does not offer a product that will protect Windows 98/NT. Those OS's are way to old to allow modern AV to work and protect your data. I don't  think there is a security product out there that will be able to protect these vulnerable OS's, IMO.

Symantec Critical System Protection IS ONE of the only security products that directly supports older NT/XP. It specifically support NT  and is about the only solution out there to harden an NT system. A security administrator can almost throw out "virus scanning" in NT as no security patches have been released for this older OS for some time (a long time actually). The solution is to lock down these machines as much as possible with CSP to thwart potential attacks and even zero day attacks automatically. Your best solution for NT is CSP period (if configured appropriately). This gives you at the least the ability to lock down the machine to make it less vulnerable to attacks and viruses, solving the attack vector proactively rather than after-the-fact AV (some vendors support "scanning" NT but that still means the malware is already on the machine). In fact the new release of CSP 5.2.6 actually includes new features to cover XPe (embedded) and continues to support fully Windows XP. If you still have workstations with 98 then I believe that to be more of a business problem than a security issue. I understand some legacy apps only running on NT however there is no reason why a workstation should be on a non-supported OS.

CSP has a seperate binary for NT agent install and all info can be obtained through product documentation.