There is usually a way to update your browser from within the application or you may use these links:
Internet Explorer Mac & Windows (at your own risk). Will be routinely upgraded when you run Windows Update.
Netscape Mac & Windows (Versions after 6.0 may be buggy on some Macs).
Mozilla Mac & Windows also Firefox: Mac OS X & Windows.
Opera Mac & Windows.
iCab Macs only (The only "modern" browser for old 68K Macs).
Camino Getting raves. Mac OS X only.
Windows users: Download the current version of Firefox and set it as your default browser. Keep Internet Explorer on your disk only to run Windows Updates.
Macintosh users of the Classic OS, Download iCab and set it as your default browser. Use Internet Explorer 5.1 only for situations where iCab won't work. OS X users can use Safari which is a perfectly good browser, or download Firefox.