jandal, what version of IE do you have installed? If IE 6, you can't go any higher with Win 98. If you open IE, click on Help, About Internet Explorer, what version is shown, and what Cipher Strength?
Can you logon to websites using secure mode (https, not http), such as banking? If you go to Tools, Internet Options, Advanced, and scroll down to Security, are boxes for "Use SSL 2.0" and "Use SSL 3.0" checked? Can you find more detailed info on Symantec's site about the browser requirements?
And, as patio mentioned, now would be a good time to switch to another anti-virus program.