purvis
Download an old (compatible) version of Firefox & install it on the Windows 2000 workstation.
Google for old versions, they are hosted at many places.
See if that accesses SME server OK.
Depending on the outcome, then you can start pointing the finger of blame more accurately.
Have you looked at log files, what error message do you receive.
You cannot just say it does not work, you need to provide better information than that if you expect help.
For example, if you have a registered domain name (on the SME server) & that is on root server lists re https access, then IE will need the root server list updated, & that may be an issue if Microsoft are no longer releasing those sort of updates for IE6 (which I suspect they are not).
Usually you can add your server domain to the browser root store, BUT you do not give us any clues as to what your problem is, so please start doing some investigation of the facts (which you have in the log files & in the error messages).